diff --git a/crates/erp-ai/Cargo.toml b/crates/erp-ai/Cargo.toml
index a087f91..3bf8ad9 100644
--- a/crates/erp-ai/Cargo.toml
+++ b/crates/erp-ai/Cargo.toml
@@ -23,4 +23,5 @@ reqwest.workspace = true
 handlebars.workspace = true
 dashmap.workspace = true
 sha2.workspace = true
+redis.workspace = true
 hex.workspace = true
diff --git a/crates/erp-ai/src/service/cache.rs b/crates/erp-ai/src/service/cache.rs
new file mode 100644
index 0000000..5ecad86
--- /dev/null
+++ b/crates/erp-ai/src/service/cache.rs
@@ -0,0 +1,244 @@
+use redis::AsyncCommands;
+use sea_orm::{ColumnTrait, EntityTrait, QueryFilter};
+use sha2::{Digest, Sha256};
+use std::time::Duration;
+use uuid::Uuid;
+
+use crate::entity::ai_analysis;
+use crate::error::AiResult;
+
+#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
+pub struct CacheKey {
+    pub tenant_id: Uuid,
+    pub analysis_type: String,
+    pub input_hash: String,
+    pub prompt_version: i32,
+}
+
+impl CacheKey {
+    pub fn new(tenant_id: Uuid, analysis_type: &str, input: &serde_json::Value, prompt_version: i32) -> Self {
+        let canonical = serde_json::to_string(input).unwrap_or_default();
+        let mut hasher = Sha256::new();
+        hasher.update(canonical.as_bytes());
+        let hash = hex::encode(hasher.finalize());
+
+        Self {
+            tenant_id,
+            analysis_type: analysis_type.to_string(),
+            input_hash: hash,
+            prompt_version,
+        }
+    }
+
+    pub fn redis_key(&self) -> String {
+        format!(
+            "ai:cache:{}:{}:{}:{}",
+            self.tenant_id, self.analysis_type, self.input_hash, self.prompt_version
+        )
+    }
+}
+
+#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
+pub struct CachedAnalysis {
+    pub analysis_id: Uuid,
+    pub content: String,
+    pub metadata: Option<serde_json::Value>,
+    pub cached_at: chrono::DateTime<chrono::Utc>,
+    pub is_degraded: bool,
+}
+
+pub struct CacheService {
+    redis: redis::Client,
+    db: sea_orm::DatabaseConnection,
+    default_ttl: Duration,
+}
+
+impl CacheService {
+    pub fn new(redis: redis::Client, db: sea_orm::DatabaseConnection, default_ttl: Duration) -> Self {
+        Self { redis, db, default_ttl }
+    }
+
+    pub async fn get(&self, key: &CacheKey) -> AiResult<Option<CachedAnalysis>> {
+        let redis_key = key.redis_key();
+
+        // L1: Redis 查询
+        match self.try_redis_get(&redis_key).await {
+            Ok(Some(cached)) => return Ok(Some(cached)),
+            Ok(None) => {}
+            Err(e) => {
+                tracing::warn!(error = %e, "Redis 缓存查询失败，降级到 DB");
+            }
+        }
+
+        // L2: DB 查询（复用现有 SHA-256 hash 逻辑）
+        let db_result = ai_analysis::Entity::find()
+            .filter(ai_analysis::Column::TenantId.eq(key.tenant_id))
+            .filter(ai_analysis::Column::InputDataHash.eq(&key.input_hash))
+            .filter(ai_analysis::Column::PromptVersion.eq(key.prompt_version))
+            .filter(ai_analysis::Column::Status.eq("completed"))
+            .filter(ai_analysis::Column::DeletedAt.is_null())
+            .one(&self.db)
+            .await?;
+
+        if let Some(record) = db_result {
+            let cached = CachedAnalysis {
+                analysis_id: record.id,
+                content: record.result_content.clone().unwrap_or_default(),
+                metadata: record.result_metadata.clone(),
+                cached_at: record.created_at,
+                is_degraded: false,
+            };
+
+            // 回填 Redis
+            if let Err(e) = self.try_redis_set(&redis_key, &cached).await {
+                tracing::warn!(error = %e, "Redis 缓存回填失败");
+            }
+
+            return Ok(Some(cached));
+        }
+
+        Ok(None)
+    }
+
+    pub async fn set(&self, key: &CacheKey, value: &CachedAnalysis) -> AiResult<()> {
+        let redis_key = key.redis_key();
+
+        // 写 Redis
+        if let Err(e) = self.try_redis_set(&redis_key, value).await {
+            tracing::warn!(error = %e, "Redis 缓存写入失败");
+        }
+
+        Ok(())
+    }
+
+    pub async fn invalidate_tenant(&self, tenant_id: Uuid) -> AiResult<u64> {
+        let pattern = format!("ai:cache:{}:*", tenant_id);
+        match self.try_redis_scan_del(&pattern).await {
+            Ok(count) => Ok(count),
+            Err(e) => {
+                tracing::warn!(error = %e, "Redis 缓存失效失败");
+                Ok(0)
+            }
+        }
+    }
+
+    async fn try_redis_get(&self, key: &str) -> redis::RedisResult<Option<CachedAnalysis>> {
+        let mut conn = self.redis.get_multiplexed_async_connection().await?;
+        let data: Option<String> = conn.get(key).await?;
+        match data {
+            Some(json) => {
+                let cached: CachedAnalysis = serde_json::from_str(&json)
+                    .map_err(|e| redis::RedisError::from((
+                        redis::ErrorKind::TypeError,
+                        "反序列化失败",
+                        e.to_string(),
+                    )))?;
+                Ok(Some(cached))
+            }
+            None => Ok(None),
+        }
+    }
+
+    async fn try_redis_set(&self, key: &str, value: &CachedAnalysis) -> redis::RedisResult<()> {
+        let mut conn = self.redis.get_multiplexed_async_connection().await?;
+        let json = serde_json::to_string(value).map_err(|e| redis::RedisError::from((
+            redis::ErrorKind::TypeError,
+            "序列化失败",
+            e.to_string(),
+        )))?;
+        let (): () = conn.set_ex(key, json, self.default_ttl.as_secs() as u64).await?;
+        Ok(())
+    }
+
+    async fn try_redis_scan_del(&self, pattern: &str) -> redis::RedisResult<u64> {
+        let mut conn = self.redis.get_multiplexed_async_connection().await?;
+        let mut count = 0u64;
+        let mut cursor: u64 = 0;
+        loop {
+            let (new_cursor, keys): (u64, Vec<String>) =
+                redis::cmd("SCAN")
+                    .arg(cursor)
+                    .arg("MATCH")
+                    .arg(pattern)
+                    .arg("COUNT")
+                    .arg(100)
+                    .query_async(&mut conn)
+                    .await?;
+            if !keys.is_empty() {
+                let del_count: u64 = conn.del(&keys).await?;
+                count += del_count;
+            }
+            cursor = new_cursor;
+            if cursor == 0 {
+                break;
+            }
+        }
+        Ok(count)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn cache_key_format() {
+        let key = CacheKey {
+            tenant_id: Uuid::parse_str("00000000-0000-0000-0000-000000000001").unwrap(),
+            analysis_type: "lab_report".into(),
+            input_hash: "abc123".into(),
+            prompt_version: 1,
+        };
+        assert_eq!(
+            key.redis_key(),
+            "ai:cache:00000000-0000-0000-0000-000000000001:lab_report:abc123:1"
+        );
+    }
+
+    #[test]
+    fn cache_key_from_input() {
+        let input = serde_json::json!({"hemoglobin": 120});
+        let key = CacheKey::new(
+            Uuid::parse_str("00000000-0000-0000-0000-000000000001").unwrap(),
+            "trend",
+            &input,
+            2,
+        );
+        assert!(key.input_hash.len() == 64);
+        assert_eq!(key.analysis_type, "trend");
+        assert_eq!(key.prompt_version, 2);
+        assert!(key.redis_key().starts_with("ai:cache:"));
+    }
+
+    #[test]
+    fn cached_analysis_serde_roundtrip() {
+        let cached = CachedAnalysis {
+            analysis_id: Uuid::now_v7(),
+            content: "血红蛋白偏低".into(),
+            metadata: Some(serde_json::json!({"model": "claude"})),
+            cached_at: chrono::Utc::now(),
+            is_degraded: false,
+        };
+        let json = serde_json::to_string(&cached).unwrap();
+        let back: CachedAnalysis = serde_json::from_str(&json).unwrap();
+        assert_eq!(back.content, "血红蛋白偏低");
+        assert!(!back.is_degraded);
+    }
+
+    #[test]
+    fn same_input_same_hash() {
+        let input = serde_json::json!({"test": 1});
+        let key1 = CacheKey::new(Uuid::now_v7(), "lab", &input, 1);
+        let key2 = CacheKey::new(Uuid::now_v7(), "lab", &input, 1);
+        assert_eq!(key1.input_hash, key2.input_hash);
+    }
+
+    #[test]
+    fn different_input_different_hash() {
+        let input1 = serde_json::json!({"test": 1});
+        let input2 = serde_json::json!({"test": 2});
+        let key1 = CacheKey::new(Uuid::now_v7(), "lab", &input1, 1);
+        let key2 = CacheKey::new(Uuid::now_v7(), "lab", &input2, 1);
+        assert_ne!(key1.input_hash, key2.input_hash);
+    }
+}
diff --git a/crates/erp-ai/src/service/mod.rs b/crates/erp-ai/src/service/mod.rs
index b4b4b80..8c23d09 100644
--- a/crates/erp-ai/src/service/mod.rs
+++ b/crates/erp-ai/src/service/mod.rs
@@ -1,5 +1,6 @@
 pub mod analysis;
 pub mod auto_analysis;
+pub mod cache;
 pub mod comparison;
 pub mod dialysis_risk_scorer;
 pub mod local_rules;
diff --git a/crates/erp-ai/src/state.rs b/crates/erp-ai/src/state.rs
index 78c7a9c..ddbc95f 100644
--- a/crates/erp-ai/src/state.rs
+++ b/crates/erp-ai/src/state.rs
@@ -6,6 +6,7 @@ use sea_orm::DatabaseConnection;
 
 use crate::provider::registry::ProviderRegistry;
 use crate::service::analysis::AnalysisService;
+use crate::service::cache::CacheService;
 use crate::service::prompt::PromptService;
 use crate::service::quota::QuotaService;
 use crate::service::suggestion::SuggestionService;
@@ -22,4 +23,5 @@ pub struct AiState {
     pub health_provider: Arc<dyn HealthDataProvider>,
     pub provider_registry: Arc<ProviderRegistry>,
     pub quota: Arc<QuotaService>,
+    pub cache: Arc<CacheService>,
 }
diff --git a/crates/erp-server/src/main.rs b/crates/erp-server/src/main.rs
index 2fc481b..7a0b8fa 100644
--- a/crates/erp-server/src/main.rs
+++ b/crates/erp-server/src/main.rs
@@ -535,6 +535,12 @@ async fn main() -> anyhow::Result<()> {
             db.clone(),
             config.ai.quota_check_enabled,
         ));
+        let cache_ttl = std::time::Duration::from_secs(config.ai.cache_ttl_seconds);
+        let cache = std::sync::Arc::new(erp_ai::service::cache::CacheService::new(
+            redis_client.clone(),
+            db.clone(),
+            cache_ttl,
+        ));
 
         erp_ai::AiState {
             db: db.clone(),
@@ -546,6 +552,7 @@ async fn main() -> anyhow::Result<()> {
             health_provider,
             provider_registry: registry,
             quota,
+            cache,
         }
     };