It's no use crying over spilt milk.

cry over spilt milk=cry over spilled milk
意为:后悔无益；既往不咎；于事无补.
例子：
1.After the baby tore up Sue's picture book,Sue'smother told her there was no use crying over spilled milk（小娃娃撕碎了苏的图书后,苏的母亲告诉苏现在哭也于事无补）
2.You have lost the game but don't cry over spilt milk.(这场比赛你已经输了,不必再做于事无补的抱怨了)