一是时态不能改变;二是变为被动语态后，谓语动词要和被动语态的主语在人称、数上保持一致。还要作如下变动：把主动语态的宾语变为被动语态的主语;主动语态的主语放在by的后面，组成介词短语，再把这个介词短语放在被动语态的谓语动词之后。在动作的执行者无须说明或不必要强调时，by短语可以省略。例如，

They will open a new supermarket there soon. 他们很快将在那里开办个新超市。

A new supermarket will be opened there soon. 一个新超市不久将在那里开办。

The doctor gave two lectures in English. 那位医生用英语讲了两次课

Two lectures were given by the doctor in English. 由那位医生用英语讲了两次课。

Somebody has warned us to be careful of rats. 有人警告我们要当心老鼠。

We have been warned to be careful of rats. 我们受到警告，要当心老鼠

如果主动语态有两个宾语(直接宾语和间接宾语)，变为被动语态时，可将其中任何一个宾语变为主语，另一个不变。但较常见的是将间接宾语变为被动语态的主语。

The reporters asked the president some questions. 记者们问了总统一些问题。

The president was asked some questions by the reporters. ( 变间接宾语为主语)

Some questions were asked the president by the reporters. (变直接宾语为主语)

We have given him a job. 我们已给了他一个工作。

He has been given a job. (变间接宾语为主语)

A job has been given (to) him. (变直接宾语为主语)