be going to,will和be doing区别

be going to 表示近期就要发生的事情,will 表示的将来时间则较远一些,如：

He is going to write a letter tonight.

He will write a book one day.

2.be going to 表示根据主观判断将来肯定发生的事情,will表示客观上将来要发生的事情.

He is seriously ill.He is going to die.

He will be twenty years old.

3.be going to 含有“计划,准备”的意思,而 will 则没有这个意思,如：

She is going to lend us her book.

He will be here in half an hour.

4.在有条件从句的主句中,一般不用 be going to,而多用will,如：

If any beasts comes at you,I'll stay with you and help you.


be doing 主要是当动词是go ,come leave,move ,start,arrive fly 等的时候用,
如：He is going to school tomorrow
I am coming.
She is flying to Beijing .

前两个是一般将来时 表示一个动作还没有发生
后一个是正在进行时 表示一个动作正在发生 完全不用的两个时态