diff --git a/datetime/datetime.go b/datetime/datetime.go
index 3b55fce..2c00dbd 100644
--- a/datetime/datetime.go
+++ b/datetime/datetime.go
@@ -190,3 +190,18 @@ func EndOfYear(t time.Time) time.Time {
 func IsLeapYear(year int) bool {
 	return year%4 == 0 && (year%100 != 0 || year%400 == 0)
 }
+
+// BetweenSeconds returns the number of seconds between two times.
+func BetweenSeconds(t1 time.Time, t2 time.Time) int64 {
+	index := t2.Unix() - t1.Unix()
+	return index
+}
+
+// DayOfYear returns which day of the year the parameter date `t` is.
+func DayOfYear(t time.Time) int {
+	y, m, d := t.Date()
+	firstDay := time.Date(y, 1, 1, 0, 0, 0, 0, t.Location())
+	nowDate := time.Date(y, m, d, 0, 0, 0, 0, t.Location())
+
+	return int(nowDate.Sub(firstDay).Hours() / 24)
+}
diff --git a/datetime/datetime_test.go b/datetime/datetime_test.go
index 9b21a6f..85d5f18 100644
--- a/datetime/datetime_test.go
+++ b/datetime/datetime_test.go
@@ -254,3 +254,32 @@ func TestIsLeapYear(t *testing.T) {
 	assert.Equal(true, result1)
 	assert.Equal(false, result2)
 }
+
+func TestBetweenSeconds(t *testing.T) {
+	assert := internal.NewAssert(t, "TestBetweenSeconds")
+
+	today := time.Now()
+	tomorrow := AddDay(today, 1)
+	yesterday := AddDay(today, -1)
+
+	result1 := BetweenSeconds(today, tomorrow)
+	result2 := BetweenSeconds(today, yesterday)
+
+	assert.Equal(int64(86400), result1)
+	assert.Equal(int64(-86400), result2)
+}
+
+func TestDayOfYear(t *testing.T) {
+	assert := internal.NewAssert(t, "TestDayOfYear")
+	date1 := time.Date(2023, 02, 01, 1, 1, 1, 0, time.Local)
+	result1 := DayOfYear(date1)
+	assert.Equal(31, result1)
+
+	date2 := time.Date(2023, 01, 02, 1, 1, 1, 0, time.Local)
+	result2 := DayOfYear(date2)
+	assert.Equal(1, result2)
+
+	date3 := time.Date(2023, 01, 01, 1, 1, 1, 0, time.Local)
+	result3 := DayOfYear(date3)
+	assert.Equal(0, result3)
+}
diff --git a/docs/datetime.md b/docs/datetime.md
index 779c332..a54b85f 100644
--- a/docs/datetime.md
+++ b/docs/datetime.md
@@ -54,6 +54,8 @@ import (
 -   [ToFormatForTpl](#ToFormatForTpl)
 -   [ToIso8601](#ToIso8601)
 -   [IsLeapYear](#IsLeapYear)
+-   [BetweenSeconds](#BetweenSeconds)
+-   [DayOfYear](#DayOfYear)
 
 <div STYLE="page-break-after: always;"></div>
 
@@ -995,3 +997,82 @@ func main() {
     // false
 }
 ```
+
+### <span id="BetweenSeconds">BetweenSeconds</span>
+
+<p>Return the number of seconds between two times.</p>
+
+<b>Signature:</b>
+
+```go
+func BetweenSeconds(t1 time.Time, t2 time.Time) int64
+```
+
+<b>Example:</b>
+
+```go
+package main
+
+import (
+    "fmt"
+    "github.com/duke-git/lancet/datetime"
+)
+
+func main() {
+    today := time.Now()
+    tomorrow := AddDay(today, 1)
+    yesterday := AddDay(today, -1)
+
+    result1 := datetime.BetweenSeconds(today, tomorrow)
+    result2 := datetime.BetweenSeconds(today, yesterday)
+
+    fmt.Println(result1)
+    fmt.Println(result2)
+
+    // Output:
+    // 86400
+    // -86400
+}
+```
+
+
+### <span id="DayOfYear">DayOfYear</span>
+
+<p>Returns which day of the year the parameter date `t` is.</p>
+
+<b>Signature:</b>
+
+```go
+func DayOfYear(t time.Time) int
+```
+
+<b>Example:</b>
+
+```go
+package main
+
+import (
+    "fmt"
+    "github.com/duke-git/lancet/datetime"
+)
+
+func main() {
+    date1 := time.Date(2023, 02, 01, 1, 1, 1, 0, time.Local)
+    result1 := datetime.DayOfYear(date1)
+
+    date2 := time.Date(2023, 01, 02, 1, 1, 1, 0, time.Local)
+    result2 := datetime.DayOfYear(date2)
+
+    date3 := time.Date(2023, 01, 01, 1, 1, 1, 0, time.Local)
+    result3 := datetime.DayOfYear(date3)
+
+    fmt.Println(result1)
+    fmt.Println(result2)
+    fmt.Println(result3)
+
+    // Output:
+    // 31
+    // 1
+    // 0
+}
+```
diff --git a/docs/datetime_zh-CN.md b/docs/datetime_zh-CN.md
index 511efa9..53f786e 100644
--- a/docs/datetime_zh-CN.md
+++ b/docs/datetime_zh-CN.md
@@ -54,6 +54,8 @@ import (
 -   [ToFormatForTpl](#ToFormatForTpl)
 -   [ToIso8601](#ToIso8601)
 -   [IsLeapYear](#IsLeapYear)
+-   [BetweenSeconds](#BetweenSeconds)
+-   [DayOfYear](#DayOfYear)
 
 <div STYLE="page-break-after: always;"></div>
 
@@ -995,3 +997,81 @@ func main() {
     // false
 }
 ```
+
+### <span id="BetweenSeconds">BetweenSeconds</span>
+
+<p>返回两个时间的间隔秒数。</p>
+
+<b>函数签名:</b>
+
+```go
+func BetweenSeconds(t1 time.Time, t2 time.Time) int64
+```
+
+<b>示例:</b>
+
+```go
+package main
+
+import (
+    "fmt"
+    "github.com/duke-git/lancet/datetime"
+)
+
+func main() {
+    today := time.Now()
+    tomorrow := AddDay(today, 1)
+    yesterday := AddDay(today, -1)
+
+    result1 := datetime.BetweenSeconds(today, tomorrow)
+    result2 := datetime.BetweenSeconds(today, yesterday)
+
+    fmt.Println(result1)
+    fmt.Println(result2)
+
+    // Output:
+    // 86400
+    // -86400
+}
+```
+
+### <span id="DayOfYear">DayOfYear</span>
+
+<p>返回参数日期是一年中的第几天。</p>
+
+<b>函数签名:</b>
+
+```go
+func DayOfYear(t time.Time) int
+```
+
+<b>示例:</b>
+
+```go
+package main
+
+import (
+    "fmt"
+    "github.com/duke-git/lancet/datetime"
+)
+
+func main() {
+    date1 := time.Date(2023, 02, 01, 1, 1, 1, 0, time.Local)
+    result1 := datetime.DayOfYear(date1)
+
+    date2 := time.Date(2023, 01, 02, 1, 1, 1, 0, time.Local)
+    result2 := datetime.DayOfYear(date2)
+
+    date3 := time.Date(2023, 01, 01, 1, 1, 1, 0, time.Local)
+    result3 := datetime.DayOfYear(date3)
+
+    fmt.Println(result1)
+    fmt.Println(result2)
+    fmt.Println(result3)
+
+    // Output:
+    // 31
+    // 1
+    // 0
+}
+```