在通常情况下，引导宾语从句的连词that 是可以省略的。如：

I know (that) she is under thirty. 我知道她不到三十岁。

I think (that) Diana will pass the exam. 我想戴安娜考试会及格的。

She says (that) she is coming to London next week. 她说她下周要来伦敦。

但在以下几种特殊情况，引导宾语从句的连词that 不能省略：

1. 当为了强调把that引导的宾语从句可位于句首时，that不能省略。如：

That she is a good girl I know. 她是一个好姑娘，我是知道的。

That he ever said such a thing I simply don’t believe. 我简直不相信他曾说过这样的话。

2. 当that从句与动词被其他词或从句隔开时，that一般不宜省略，以免造成语义混乱。如：

They told us once again that the situation was serious.他们又一次告诉我们说形势是严重的。

The dealer told me how much he was prepared to pay for my car and that I could have the money without delay. 那个商人告诉我他准备出多少钱买我的汽车，并说我会立即收到款。

3. 当两个或多个that引导的宾语从句并列使用时，即使省略了第一个从句的引导词that，后面的that也不可省略。如：

He said (that) he couldn’t tell you right away and that you wouldn’t understand. 他说他不能马上告诉你，你是不会理解的。

He said (that) it wasn’t his business and that the government should do something about it. 他说这不关他的事，而是政府应该对这事想点办法。

引用地址: http://www.yygrammar.com/Article/201104/2163.html