diff --git a/datetime/datetime.go b/datetime/datetime.go
index 50101ee..2636c4b 100644
--- a/datetime/datetime.go
+++ b/datetime/datetime.go
@@ -237,3 +237,10 @@ func BetweenSeconds(t1 time.Time, t2 time.Time) int64 {
 	index := t2.Unix() - t1.Unix()
 	return index
 }
+
+func DayOfYear(t1 time.Time) int {
+	y, m, d := t1.Date()
+	firstDay := time.Date(y, 1, 1, 0, 0, 0, 0, t1.Location())
+	nowDate := time.Date(y, m, d, 0, 0, 0, 0, t1.Location())
+	return int(nowDate.Sub(firstDay).Hours() / 24)
+}
diff --git a/datetime/datetime_test.go b/datetime/datetime_test.go
index 4314564..d92fe19 100644
--- a/datetime/datetime_test.go
+++ b/datetime/datetime_test.go
@@ -271,3 +271,18 @@ func TestIsLeapYear(t *testing.T) {
 	assert.Equal(true, result1)
 	assert.Equal(false, result2)
 }
+
+func TestDayOfYear(t *testing.T) {
+	assert := internal.NewAssert(t, "TestDayOfYear")
+	date := time.Date(2023, 02, 01, 1, 1, 1, 0, time.Local)
+	result := DayOfYear(date)
+	assert.Equal(31, result)
+
+	date1 := time.Date(2023, 01, 02, 1, 1, 1, 0, time.Local)
+	result1 := DayOfYear(date1)
+	assert.Equal(1, result1)
+
+	date3 := time.Date(2023, 01, 01, 1, 1, 1, 0, time.Local)
+	result2 := DayOfYear(date3)
+	assert.Equal(0, result2)
+}