diff --git a/crates/erp-ai/src/service/mod.rs b/crates/erp-ai/src/service/mod.rs
index 3319347..b4b4b80 100644
--- a/crates/erp-ai/src/service/mod.rs
+++ b/crates/erp-ai/src/service/mod.rs
@@ -6,6 +6,7 @@ pub mod local_rules;
 pub mod output_parser;
 pub mod post_process;
 pub mod prompt;
+pub mod quota;
 pub mod reanalysis;
 pub mod suggestion;
 pub mod usage;
diff --git a/crates/erp-ai/src/service/quota.rs b/crates/erp-ai/src/service/quota.rs
new file mode 100644
index 0000000..d2e0505
--- /dev/null
+++ b/crates/erp-ai/src/service/quota.rs
@@ -0,0 +1,188 @@
+use sea_orm::{ColumnTrait, EntityTrait, FromQueryResult, QueryFilter, Statement};
+use uuid::Uuid;
+
+use crate::entity::ai_tenant_config;
+use crate::error::{AiError, AiResult};
+
+pub struct QuotaService {
+    db: sea_orm::DatabaseConnection,
+    enabled: bool,
+}
+
+impl QuotaService {
+    pub fn new(db: sea_orm::DatabaseConnection, enabled: bool) -> Self {
+        Self { db, enabled }
+    }
+
+    pub async fn get_tenant_config(
+        &self,
+        tenant_id: Uuid,
+    ) -> AiResult<Option<ai_tenant_config::Model>> {
+        let config = ai_tenant_config::Entity::find()
+            .filter(ai_tenant_config::Column::TenantId.eq(tenant_id))
+            .filter(ai_tenant_config::Column::DeletedAt.is_null())
+            .filter(ai_tenant_config::Column::IsEnabled.eq(true))
+            .one(&self.db)
+            .await?;
+        Ok(config)
+    }
+
+    pub async fn check_quota(
+        &self,
+        tenant_id: Uuid,
+        patient_id: Option<Uuid>,
+    ) -> AiResult<()> {
+        if !self.enabled {
+            return Ok(());
+        }
+
+        let config = match self.get_tenant_config(tenant_id).await? {
+            Some(c) => c,
+            None => return Ok(()),
+        };
+
+        let month_usage = self.get_monthly_token_usage(tenant_id).await?;
+        if month_usage >= config.monthly_token_budget {
+            return Err(AiError::QuotaExhausted {
+                tenant_id,
+                reason: format!(
+                    "月度 Token 预算已耗尽 ({}/{})",
+                    month_usage, config.monthly_token_budget
+                ),
+            });
+        }
+
+        if let Some(pid) = patient_id {
+            let daily_count = self.get_daily_patient_count(tenant_id, pid).await?;
+            if daily_count >= config.daily_patient_limit as i64 {
+                return Err(AiError::QuotaExhausted {
+                    tenant_id,
+                    reason: format!(
+                        "患者 {} 今日分析次数已达上限 ({}/{})",
+                        pid, daily_count, config.daily_patient_limit
+                    ),
+                });
+            }
+        }
+
+        Ok(())
+    }
+
+    async fn get_monthly_token_usage(&self, tenant_id: Uuid) -> AiResult<i64> {
+        #[derive(Debug, FromQueryResult)]
+        struct TokenSum {
+            total_tokens: i64,
+        }
+
+        let sql = r#"
+            SELECT COALESCE(SUM(input_tokens + output_tokens), 0) AS total_tokens
+            FROM ai_usage
+            WHERE tenant_id = $1
+              AND created_at >= date_trunc('month', CURRENT_DATE)
+        "#;
+
+        let result: Option<TokenSum> = TokenSum::find_by_statement(
+            Statement::from_sql_and_values(
+                sea_orm::DatabaseBackend::Postgres,
+                sql,
+                [tenant_id.into()],
+            ),
+        )
+        .one(&self.db)
+        .await?;
+
+        Ok(result.map(|r| r.total_tokens).unwrap_or(0))
+    }
+
+    async fn get_daily_patient_count(
+        &self,
+        tenant_id: Uuid,
+        patient_id: Uuid,
+    ) -> AiResult<i64> {
+        #[derive(Debug, FromQueryResult)]
+        struct CountResult {
+            count: i64,
+        }
+
+        let sql = r#"
+            SELECT COUNT(*) AS count
+            FROM ai_analysis_results
+            WHERE tenant_id = $1
+              AND patient_id = $2
+              AND deleted_at IS NULL
+              AND created_at >= CURRENT_DATE
+        "#;
+
+        let result: Option<CountResult> = CountResult::find_by_statement(
+            Statement::from_sql_and_values(
+                sea_orm::DatabaseBackend::Postgres,
+                sql,
+                [tenant_id.into(), patient_id.into()],
+            ),
+        )
+        .one(&self.db)
+        .await?;
+
+        Ok(result.map(|r| r.count).unwrap_or(0))
+    }
+
+    pub async fn get_usage_summary(
+        &self,
+        tenant_id: Uuid,
+    ) -> AiResult<QuotaSummary> {
+        let config = self.get_tenant_config(tenant_id).await?;
+        let budget = config
+            .as_ref()
+            .map(|c| c.monthly_token_budget)
+            .unwrap_or(1_000_000);
+
+        let used = self.get_monthly_token_usage(tenant_id).await?;
+
+        Ok(QuotaSummary {
+            tenant_id,
+            monthly_budget: budget,
+            monthly_used: used,
+            daily_patient_limit: config
+                .as_ref()
+                .map(|c| c.daily_patient_limit)
+                .unwrap_or(50),
+        })
+    }
+}
+
+#[derive(Debug, Clone, serde::Serialize)]
+pub struct QuotaSummary {
+    pub tenant_id: Uuid,
+    pub monthly_budget: i64,
+    pub monthly_used: i64,
+    pub daily_patient_limit: i32,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn quota_summary_serialization() {
+        let summary = QuotaSummary {
+            tenant_id: Uuid::now_v7(),
+            monthly_budget: 1_000_000,
+            monthly_used: 250_000,
+            daily_patient_limit: 50,
+        };
+        let json = serde_json::to_value(&summary).unwrap();
+        assert_eq!(json["monthly_budget"], 1_000_000);
+        assert_eq!(json["monthly_used"], 250_000);
+    }
+
+    #[test]
+    fn quota_error_contains_reason() {
+        let tid = Uuid::now_v7();
+        let err = AiError::QuotaExhausted {
+            tenant_id: tid,
+            reason: "月度预算耗尽".into(),
+        };
+        let msg = err.to_string();
+        assert!(msg.contains("月度预算耗尽"));
+    }
+}