diff --git a/tasks/watergroup/month.go b/tasks/watergroup/month.go
index b8ff4a05..971df23e 100644
--- a/tasks/watergroup/month.go
+++ b/tasks/watergroup/month.go
@@ -79,7 +79,7 @@ func dealMonth(gid string) {
 	var medianCount int64
 	for idx, v := range records {
 		msgCount += v.Count
-		if idx == len(records)/2 {
+		if idx == (len(records)/2)-1 {
 			medianCount = v.Count
 		}
 	}
diff --git a/tasks/watergroup/week.go b/tasks/watergroup/week.go
index f2daa61f..b8df0c95 100644
--- a/tasks/watergroup/week.go
+++ b/tasks/watergroup/week.go
@@ -78,7 +78,7 @@ func dealWeek(gid string) {
 	var medianCount int64
 	for idx, v := range records {
 		msgCount += v.Count
-		if idx == len(records)/2 {
+		if idx == (len(records)/2)-1 {
 			medianCount = v.Count
 		}
 	}
diff --git a/tasks/watergroup/year.go b/tasks/watergroup/year.go
index d3c94b08..aba255a1 100644
--- a/tasks/watergroup/year.go
+++ b/tasks/watergroup/year.go
@@ -78,7 +78,7 @@ func dealYear(gid string) {
 	var medianCount int64
 	for idx, v := range records {
 		msgCount += v.Count
-		if idx == len(records)/2 {
+		if idx == (len(records)/2)-1 {
 			medianCount = v.Count
 		}
 	}
diff --git a/tasks/watergroup/yesterday.go b/tasks/watergroup/yesterday.go
index 184a1e16..b932756a 100644
--- a/tasks/watergroup/yesterday.go
+++ b/tasks/watergroup/yesterday.go
@@ -80,7 +80,7 @@ func dealYesterday(gid string) {
 	var medianCount int64
 	for idx, v := range records {
 		msgCount += v.Count
-		if idx == len(records)/2 {
+		if idx == (len(records)/2)-1 {
 			medianCount = v.Count
 		}
 	}