diff --git a/internal/logic/monitor/api_metrics.go b/internal/logic/monitor/api_metrics.go
index 6759a47..9b233ef 100644
--- a/internal/logic/monitor/api_metrics.go
+++ b/internal/logic/monitor/api_metrics.go
@@ -64,13 +64,22 @@ type trafficFlowRow struct {
 // normalizeMonitorDateRange 规范化监控类接口的日期范围，返回 YYYY-MM-DD 的 [start, end]（含）。
 // 缺省近 30 天；end 不超过今天；跨度上限 trafficFlowMaxDays。流量桑基图与模型性能共用。
 func normalizeMonitorDateRange(startDate, endDate string) (string, string) {
+	return normalizeMonitorDateRangeAt(startDate, endDate, time.Now())
+}
+
+// normalizeMonitorDateRangeAt is separated for deterministic tests. Date-only
+// filters must be compared as calendar dates in the server's location, rather
+// than against the current instant. Otherwise, on a non-UTC server before its
+// UTC offset, today's parsed midnight can incorrectly fall after time.Now()
+// and the range silently falls back to the default 30 days.
+func normalizeMonitorDateRangeAt(startDate, endDate string, now time.Time) (string, string) {
 	const layout = "2006-01-02"
-	today := time.Now()
-	end, err := time.Parse(layout, endDate)
+	today := time.Date(now.Year(), now.Month(), now.Day(), 0, 0, 0, 0, now.Location())
+	end, err := time.ParseInLocation(layout, endDate, now.Location())
 	if err != nil || end.After(today) {
 		end = today
 	}
-	start, err := time.Parse(layout, startDate)
+	start, err := time.ParseInLocation(layout, startDate, now.Location())
 	if err != nil || start.After(end) {
 		start = end.AddDate(0, 0, -29)
 	}
diff --git a/internal/logic/monitor/api_metrics_test.go b/internal/logic/monitor/api_metrics_test.go
index 8307a2d..9ec4a9f 100644
--- a/internal/logic/monitor/api_metrics_test.go
+++ b/internal/logic/monitor/api_metrics_test.go
@@ -5,11 +5,22 @@ import (
 	"reflect"
 	"strings"
 	"testing"
+	"time"
 
 	v1 "github.com/qianfree/team-api/api/admin/v1"
 	"github.com/qianfree/team-api/internal/logic/common"
 )
 
+func TestNormalizeMonitorDateRangeKeepsTodayInNonUTCTimezone(t *testing.T) {
+	location := time.FixedZone("UTC+8", 8*60*60)
+	now := time.Date(2026, time.August, 29, 0, 10, 0, 0, location)
+
+	start, end := normalizeMonitorDateRangeAt("2026-08-29", "2026-08-29", now)
+	if start != "2026-08-29" || end != "2026-08-29" {
+		t.Fatalf("same-day range = [%s, %s], want [2026-08-29, 2026-08-29]", start, end)
+	}
+}
+
 // perfFieldValue 按 JSON 字段名（snake_case）从结构体取值，整数统一归一为 int64、
 // 浮点统一为 float64，与旧的 []map[string]any 断言口径保持一致。
 func perfFieldValue(item v1.ModelPerformanceSummary, field string) any {