diff --git a/utilities/at32f421_freertos_demo/src/TaskLoop.c b/utilities/at32f421_freertos_demo/src/TaskLoop.c
index 62cb569..7a977e5 100644
--- a/utilities/at32f421_freertos_demo/src/TaskLoop.c
+++ b/utilities/at32f421_freertos_demo/src/TaskLoop.c
@@ -665,7 +665,9 @@ void vd1_task(void)
     }
 
     /* 1b. 快速 IIR — α=0.5: (old + new) / 2 */
-    if (loop1_CAPVD_fast != 0) {
+    if (loop1_CAPVD_fast == 0) {
+        loop1_CAPVD_fast = loop1_CAPVD;  // 首次直接锁定
+    } else {
         loop1_CAPVD_fast = (loop1_CAPVD_fast + loop1_CAPVD) / 2;
     }