“白费力气或徒劳无益”用英语表达可以是 flog a dead horse 或 beat a dead horse，寓意：
1、waste energy on something that has no chance of succeeding
把精力浪费在没有成功机会的事情上
2、waste on a lost cause
在失败的事业上浪费精力
3、engaging in a fruitless effort
徒劳无功
4、attempting to revive interest in something which has died out
试图恢复人们对已经消失的东西的兴趣
解析：短语动词 die out 译为“消失，灭绝”。
例如：
1、He keeps trying to get his manuscripts published, but I think he is flogging a dead horse.
他一直想让他的手稿出版，但我认为他是白费力气。
解析：get something done 是一种使役结构，表示“让某人帮我们做某事”。
2、There's no use trying to keep this business going. We are flogging a dead horse.
想让这件事继续下去是没有用的。我们白费力气。
解析：no 作限定词，用在一个词名词或名词短语之前，no 与名词之间没有冠词，相当于 not any 或 not a/an.
3、I've told him numerous times to manage his routine , but I think I've just been flogging a dead horse.
我已经告诉他很多次了，要有效地管理他的日常事务，但我想我只是在鞭打一匹死马。
解析：
a、现在完成进行时 have been floggiing a dead horse 表示动作从过去一直持续进行到现在。
b、time 译为“次，回”的时候，是可数名词。
4、You're flogging a dead horse trying to persuade him to come with us. He hates going out at night.
你想说服他和我们一起去，真是白费力气。他讨厌晚上出去。
解析： 短语 trying to persuade hime to come with us 作状语表伴随。
5、You keep trying to convince him to join your company, I think you're flogging a dead horse. He's happy where he is.
你一直想说服他加入你的公司，但我认为你是白费力气。他在那里很开心。