动词开头什么时候加ing

1.现在分词（短语）做状语，与主语是逻辑上的主谓关系时，如：

Walking in the street，I saw my teacher. （现在分词短语 walking in the street 表示时间，即，当我走在街上的时候，walking 与主语 I 是 逻辑上的主谓关系——我走在）

Having finished my homework，I went out to play.（现在分词短语的完成时，表示原因，即，因为我做完了作业；having finished 与主语 I 是逻辑上的主谓关系——我做完了）

2.动名词（短语）做主语，表示一件事情或一个概念时，如：

Reading is my great interest. （这里的 ing 动词，是动名词，因为，它在句首做句子的主语，表示 reading 这件事儿 ）

一，动词加ing做谓语情况

做谓语时动词加ing前面必须加上be动词,形成be+动词ing(现在分词)作句子谓语，构成进行时态句子。

例如:

He is reading a book now.

他正在看书.

He was watching TV when his mother came in.

他妈妈进来时，他正在看电视。

They've been waiting for you for three hours.

他们等你三个小时了.

二，动词加ing做非谓语情况

1、动词作介词的宾语要加ing(动名词)

I'm looking forward to seeing you again.

我期盼着再次见到你.

The boy is so excited about hearing from his mother.

男孩为收到他妈妈的来信很兴奋。

2、部分动词用动词做宾语。做宾语的动词要加ing(动名词)

I Practising speaking English Every day.

我每天练习说英语.

Could you mind opening the door?

你介意开门吗？

I have finished reading three books.

我已经看完三本书.

The old man Enjoys living in the country.

这老人喜欢住在农村.

3、一些固定句式后面要加动词ing(现在分词)

We have fun Playing in the park on Sunday.

Most students have problems speaking English.

4、动词修饰名词做后置定语时，要加ing(现在分词)

There is a boy Crying over there.

I felt something moving in the house.

I heard someone singing in the next room.

5、动词做主语和表语时，动词要加ing(动名词)

Swimming is very popular in summer.

His job is teaching English.