diff --git a/backend/internal/repository/billing_cache.go b/backend/internal/repository/billing_cache.go
index 4fbdae14..6922b4c8 100644
--- a/backend/internal/repository/billing_cache.go
+++ b/backend/internal/repository/billing_cache.go
@@ -20,6 +20,11 @@ const (
 	billingCacheTTL           = 5 * time.Minute
 	billingCacheJitter        = 30 * time.Second
 	rateLimitCacheTTL         = 7 * 24 * time.Hour // 7 days matches the longest window
+
+	// Rate limit window durations — must match service.RateLimitWindow* constants.
+	rateLimitWindow5h = 5 * time.Hour
+	rateLimitWindow1d = 24 * time.Hour
+	rateLimitWindow7d = 7 * 24 * time.Hour
 )
 
 // jitteredTTL 返回带随机抖动的 TTL，防止缓存雪崩
@@ -90,17 +95,40 @@ var (
 		return 1
 	`)
 
-	// updateRateLimitUsageScript atomically increments all three rate limit usage counters.
-	// Returns 0 if the key doesn't exist (cache miss), 1 on success.
+	// updateRateLimitUsageScript atomically increments all three rate limit usage counters
+	// with window expiration checking. If a window has expired, its usage is reset to cost
+	// (instead of accumulated) and the window timestamp is updated, matching the DB-side
+	// IncrementRateLimitUsage semantics.
+	//
+	// ARGV: [1]=cost, [2]=ttl_seconds, [3]=now_unix, [4]=window_5h_seconds, [5]=window_1d_seconds, [6]=window_7d_seconds
 	updateRateLimitUsageScript = redis.NewScript(`
 		local exists = redis.call('EXISTS', KEYS[1])
 		if exists == 0 then
 			return 0
 		end
 		local cost = tonumber(ARGV[1])
-		redis.call('HINCRBYFLOAT', KEYS[1], 'usage_5h', cost)
-		redis.call('HINCRBYFLOAT', KEYS[1], 'usage_1d', cost)
-		redis.call('HINCRBYFLOAT', KEYS[1], 'usage_7d', cost)
+		local now = tonumber(ARGV[3])
+		local win5h = tonumber(ARGV[4])
+		local win1d = tonumber(ARGV[5])
+		local win7d = tonumber(ARGV[6])
+
+		-- Helper: check if window is expired and update usage + window accordingly
+		-- Returns nothing, modifies the hash in-place.
+		local function update_window(usage_field, window_field, window_duration)
+			local w = tonumber(redis.call('HGET', KEYS[1], window_field) or 0)
+			if w == 0 or (now - w) >= window_duration then
+				-- Window expired or never started: reset usage to cost, start new window
+				redis.call('HSET', KEYS[1], usage_field, tostring(cost))
+				redis.call('HSET', KEYS[1], window_field, tostring(now))
+			else
+				-- Window still valid: accumulate
+				redis.call('HINCRBYFLOAT', KEYS[1], usage_field, cost)
+			end
+		end
+
+		update_window('usage_5h', 'window_5h', win5h)
+		update_window('usage_1d', 'window_1d', win1d)
+		update_window('usage_7d', 'window_7d', win7d)
 		redis.call('EXPIRE', KEYS[1], ARGV[2])
 		return 1
 	`)
@@ -280,7 +308,15 @@ func (c *billingCache) SetAPIKeyRateLimit(ctx context.Context, keyID int64, data
 
 func (c *billingCache) UpdateAPIKeyRateLimitUsage(ctx context.Context, keyID int64, cost float64) error {
 	key := billingRateLimitKey(keyID)
-	_, err := updateRateLimitUsageScript.Run(ctx, c.rdb, []string{key}, cost, int(rateLimitCacheTTL.Seconds())).Result()
+	now := time.Now().Unix()
+	_, err := updateRateLimitUsageScript.Run(ctx, c.rdb, []string{key},
+		cost,
+		int(rateLimitCacheTTL.Seconds()),
+		now,
+		int(rateLimitWindow5h.Seconds()),
+		int(rateLimitWindow1d.Seconds()),
+		int(rateLimitWindow7d.Seconds()),
+	).Result()
 	if err != nil && !errors.Is(err, redis.Nil) {
 		log.Printf("Warning: update rate limit usage cache failed for api key %d: %v", keyID, err)
 		return err