这个问题有点大，没有好好研究过，下面是临时凑的几条，不一定全面，仅供参考：

▲如果定语从句的谓语是进行时态（包括用进行时态表示将来意义的用法），通常可以转化为现在分词或过去分词短语（括号内的词不省略为定语从 句，省略后即为现在分词短语作定语）。如：

Do you know the woman (who is) talking to Tom? 和汤姆说话的女人你认识吗? 

There were some children (who were) swimming in the river. 有些小孩在河里游泳。

I didn’t talk much to the man (who was) sitting next to me. 我没和坐在我旁边的人多讲话。

Police (who are) investigating the crime are looking for three men. 调查这件罪案的警察在找寻三个人。

但是要注意的是，并非只有谓语是进行时态的定语从句才可转化为现在分词（短语），有时一般时态也可转化为现在分词（括号前的现在分词可以括号内的定语从句来改写）。如：

It is said that those eating (=who eat) the most are the least healthy. 据说吃得最多的人身体最差。

Jim has got a brother working (=who works) in a bank in London. 吉姆有一个哥哥在伦敦的一家银行里工作。

Students wanting (=who want) more information should apply in writing. 想要得到更多资料的学生应提出书面申请。

A young man writing (=who writes) novels came to speak to us yesterday. 一位写小说的青年昨天来向我们作报告。

▲如果定语从句的谓语是一般时态的被动语态，则通常可以考虑用过去分词来改写（括号内的词不省略为定语从 句，省略后即为过去分词短语作定语）。如：

She is a dancer (who was) trained in our college. 她是我们大学培养的舞蹈演员。

The woman (who was) dressed in white is a famous actress. 那位穿白衣的女子是位有名的女演员。

There is a red car (which is) parked outside the house. 房子外边停着一辆红色汽车。

The system (which is) used in this school is very successful. 这学校使用的系统很成功。

What do you think of the play (which was) put on by the students? 学生们演的剧你觉得怎么样? 

Most of the goods (which are) made in this factory are exported. 这家工厂的产品大部分出口。

A chimney (which is) filled with soot requires the services of a qualified chimneysweep. 布满烟灰的烟囱需要合格的烟囱清扫工去清扫。

▲如果定语从句的谓语是进行时态的被动语态，则通常可考虑用现在分词的被动式来改写（括号内的词不省略为定语从 句，省略后即为现在分词的被动式作定语）。如：

The woman (who is) being operated on is his mother. 正在动手术的女人是他母亲。

He wasn’t interested in the question (which was) being discussed. 他对正在讨论的问题不感兴趣。

▲如果定语从句所表示的动作是尚未发生的动作，则可以考虑用不定式来改写。如：

I have a lot of letters which I have to write. 我有很多信要写。

=I have a lot of letters to write. 我有很多信要写。

They planned a big meeting which would be held next year. 他们为明年将要举行的一次盛大集会制定了计划。

=They planned a big meeting to be held next year. 他们为明年将要举行的一次盛大集会制定了计划。

有时定语从句的谓语并非表示一个未发生的动作，而是表示一种通常的情况。如：

He is not a man who tells a lie. 他不是个说谎的人。

=He is not a man to tell a lie. 他不是个说谎的人。

He is not a man who bows before difficulties. 他不是一个向困难低头的人。

=He is not a man to bow before difficulties. 他不是一个向困难低头的人。

▲做这些句式简化或转换时，有时要注意一些特殊结构的特殊搭配。比如，当一个名词前面有序数词修饰时，它后面的定语从句原则应用不定式（而不是现在分词）来改写。如：

He was the first man who thought of it. 他是第一个想到这一点的人。

=He was the first man to think of it. 他是第一个想到这一点的人。

Who was the first woman who climbed Eretest? 第一个登上埃佛勒斯峰的女人是谁呀? 

=Who was the first woman to climb Eretest? 第一个登上埃佛勒斯峰的女人是谁呀? 

此时如果定语从句是被动语态，则也可用过去分词。如：

She was the first person who was awarded such a prize. 她是第一个获得这种奖的人。

=She was the first person (to be) awarded such a prize. 她是第一个获得这种奖的人。