一、表达意义不同：
no sooner than，翻译为“一…就…”
hardly when ，翻译为“几乎未来得及；他的妻子就开始抱怨；刚一…就；几乎未来得及就”
as soon as，翻译为“一…就…”，语法注意主将从现。意思是尽可能的快，一般用于词组as soon as possible（缩写ASAP）。
二、它们三个所表达事情的间隔时间不同。
as soon as 较长，no sooner...than 居中，hardly...when 间隔时间最短。
1、as soon as意思相当于 A事情发生以后，就做B这件事情。
例如：I'll write you as soon as I get there.
我一到那儿就给你来信。（一般现在时）
As soon as I went in,Katherine cried out with pleasure.
我一进门，Katherine就高兴的叫起来。（一般过去时）
2、no sooner...than
它的意思相当于刚做完A这件事，就做了B这件事。
例如：He had no sooner returned than he bought a house.
他一回来就买了一套房子。
3、hardly...when...,它的意思是“几乎未来得及做完A这件事，紧接着就开始B这件事了”，使用这个短语时，一般用于过去完成时；并且when有时可改用before。例如：
He had hardly finished the article when the light went out.
他刚写完文，灯就熄了。
三、如果no sooner 位于句首，主句要用倒装结构。As soon as和hardly...when...没有这个情况。例如：
No sooner had he arrived than he went away again.
他刚到就又走了。
1.从两件事间隔的时间看，as soon as 最长，"A事发生后，就做B事"；no sooner...than 次之，"刚做完A事，就做B事"；hardly...when最短，"几乎未来得及做完A事，紧接着就做B事"。
2.as soon as较常用，在句中的位置很灵活。意思相当于“A事情发生以后，就做B这件事”。 口语和书面语都可以。特点是，在句子中的位置比较灵活，而且可以用于各种时态。例如：
I’ll write you as soon as I get there.
我一到那儿就给你来信。（一般现在时）
As soon as I went in, Katherine cried out with pleasure.
我一进门，Katherine 就高兴的叫起来。（一般过去时）
I’ll return the book as soon as I have read it.
我一读完就把书还回去。（现在完成时）
①no sooner…than意思相当于“刚做完A这件事，就做B这件事”。例如：
He had no sooner returned than he bought a house.
他一回来就买了一套房子。
②当no sooner…than的no sooner位于句首时及hardly…when…的hardly放在句首时，主句要用倒装结构。例如：
No sooner had the game started than it began to rain heavily.
运动会刚开始，天就下起了大雨。
Hardly had I finished eating when he came in.
我刚吃完他就进来了。
Hardly had she gone out when a student came to visit her.
她还没走出家门，就有一个学生来看望她。
③hardly…when...意思是“几乎未来得及做完A这件事，紧接着就开始B这件事。”例如： He had hardly had time to settle down when he sold the house.
他还未安顿下来，就卖掉了那所房子。
3.as soon as可用于各种时态；而在no sooner...than...和hardly…when…句型中，主句一般要用过去完成时，than或when后面的从句常用一般过去时。例如：
Hardly had I finished eating when he came in.
我刚吃完他就进来了。
No sooner had the game started than it began to rain heavily.
运动会刚开始，天就下起了大雨。本回答被网友采纳
no sooner than和hardly when用法基本无区别，但它和as soon as用法有区别。
一、as soon as的用法。
as soon as是一个从属连接词，意思是“一……就……”，强调两件事情紧接着发生，主句和从句用的都是同一时态，也可以表示将来的事情，这时主句用将来时，从句用一般现在时，例如：
As soon as you mentioned rain, it started pouring.
你一提到雨，就下起大雨来了。
I’ll call you as soon as I arrive home.
我一到家就给你打电话。
We’ll start the meeting as soon as the chairman comes.
主席一来，我们就开会。
He left as soon as he heard the news.
他一听到这事儿就走了。
二、hardly when与no sooner than的用法。
hardly when和no sooner than都表示“一……就……”，但主句和从句所用的时态不一样，它们都用来描述过去的事情，一般不用于将来时。它们的主句一般用过去完成时，从句要用一般过去式表示。注意两个连接词不要发生混淆，hardly要配when，有时也可以配before，no sooner因为有一个比较级sooner在里面，后面配的连接词一定是than。
如果no sooner或hardly位于句首，主句要用部分倒装结构，如：
No sooner had you mentioned rain than it started pouring.
你一提到雨，就下起大雨来了。
Hardly had he heard the news when he left.
他一听到这事儿就走了。
本回答被网友采纳