Let well alone 的 well 是个名词，意思是良好的状态。那么直译就是不要打扰那些良好的状态。综合英美一些字典的解释，得到了 Do not change or try to improve something that is not causing any problems. 就如中文的“得过且过”。转个角度来说，又有一点 GalaxySong 所说的“安于现状就已经行了”的意思。

以下是一些在网上找到的例句，可参考其中的用法：

From what I can tell, most people are members of the “Let's leave well enough alone” and “If it ain't broke, don't fix it” clubs.

I don't think it's ever a good idea to tamper with tradition. Leave well enough alone.

It is well: it works well: let well alone.

安于现状就已经行了; 维持原状
You can avoid all kinds of trouble by letting well alone.
随遇而安就能避免种种麻烦。

Leave him alone! 不要打扰他

其实'let alone'和'let well alone'的意思很不一样。

'let alone' 前一个回答是对的。

但是‘let well alone' （或者'leave well alone') 的意思是‘不要打扰‘,'不要干涉‘
比如:
'He's not in a good mood. I'd leave him well alone if I were you.'