diff --git a/internal/tools/backfill.go b/internal/tools/backfill.go
index 785589b..bc1ae48 100644
--- a/internal/tools/backfill.go
+++ b/internal/tools/backfill.go
@@ -214,17 +214,18 @@ func RunBackfill10Min(ctx context.Context, opts BackfillOptions) error {
 			$7, $8, $9,
 			$10, $11, $12, $13
 		) ON CONFLICT (station_id, bucket_start) DO UPDATE SET
-			temp_c_x100 = EXCLUDED.temp_c_x100,
-			humidity_pct = EXCLUDED.humidity_pct,
-			wind_speed_ms_x1000 = EXCLUDED.wind_speed_ms_x1000,
-			wind_gust_ms_x1000 = EXCLUDED.wind_gust_ms_x1000,
-			wind_dir_deg = EXCLUDED.wind_dir_deg,
-			rain_10m_mm_x1000 = EXCLUDED.rain_10m_mm_x1000,
-			rain_total_mm_x1000 = EXCLUDED.rain_total_mm_x1000,
-			solar_wm2_x100 = EXCLUDED.solar_wm2_x100,
-			uv_index = EXCLUDED.uv_index,
-			pressure_hpa_x100 = EXCLUDED.pressure_hpa_x100,
-			sample_count = EXCLUDED.sample_count`
+			-- 仅当新聚合样本数不小于已有样本数时才用新值覆盖均值类字段，避免回退
+			temp_c_x100 = CASE WHEN EXCLUDED.sample_count >= rs485_weather_10min.sample_count THEN EXCLUDED.temp_c_x100 ELSE rs485_weather_10min.temp_c_x100 END,
+			humidity_pct = CASE WHEN EXCLUDED.sample_count >= rs485_weather_10min.sample_count THEN EXCLUDED.humidity_pct ELSE rs485_weather_10min.humidity_pct END,
+			wind_speed_ms_x1000 = CASE WHEN EXCLUDED.sample_count >= rs485_weather_10min.sample_count THEN EXCLUDED.wind_speed_ms_x1000 ELSE rs485_weather_10min.wind_speed_ms_x1000 END,
+			wind_gust_ms_x1000 = GREATEST(rs485_weather_10min.wind_gust_ms_x1000, EXCLUDED.wind_gust_ms_x1000),
+			wind_dir_deg = CASE WHEN EXCLUDED.sample_count >= rs485_weather_10min.sample_count THEN EXCLUDED.wind_dir_deg ELSE rs485_weather_10min.wind_dir_deg END,
+			rain_10m_mm_x1000 = GREATEST(rs485_weather_10min.rain_10m_mm_x1000, EXCLUDED.rain_10m_mm_x1000),
+			rain_total_mm_x1000 = GREATEST(rs485_weather_10min.rain_total_mm_x1000, EXCLUDED.rain_total_mm_x1000),
+			solar_wm2_x100 = CASE WHEN EXCLUDED.sample_count >= rs485_weather_10min.sample_count THEN EXCLUDED.solar_wm2_x100 ELSE rs485_weather_10min.solar_wm2_x100 END,
+			uv_index = CASE WHEN EXCLUDED.sample_count >= rs485_weather_10min.sample_count THEN EXCLUDED.uv_index ELSE rs485_weather_10min.uv_index END,
+			pressure_hpa_x100 = CASE WHEN EXCLUDED.sample_count >= rs485_weather_10min.sample_count THEN EXCLUDED.pressure_hpa_x100 ELSE rs485_weather_10min.pressure_hpa_x100 END,
+			sample_count = GREATEST(rs485_weather_10min.sample_count, EXCLUDED.sample_count)`
 
 	for stationID, m := range buckets {
 		for bucketStart, ag := range m {