will/shall be doing 表将来某刻正在进行 (The train will be arriving at two o'clock.)
will/shall have done 表将来某一刻以前已完成 (eg:Before long he will have forgotten all about it.)
will/shall have been doing 表一个已经开始的动作到将来某一时间仍在进行 ( eg: By the end of next month I shalled have been working here for 20 years exactly.)
will/shall do (eg: The naxt train to Beijing will leave at8 a.m.)
be going to
表意图,打算在将来做某事(be going to的“意图”是事先经过考虑的,而will+不定式表示的“意图”则是说话时刻临时想到的。)(1.eg: A:Why are you taking down all the pictures? B: I'm going to repaper the room.2.eg: What a terribly heavy box! B: I'll help you to carry it.)
表预见,现在已有迹象表明将要发生或即将发生某种情况(eg: I feel dizzy. I'm going to faint.)
be to
按计划安排即将发生的动作 (eg: There's to be an investigation.)
表命令,禁止或可能性等 (eg: You are to stand here.Do you understand?)
be about to 表最近或马上要发生的动作 (eg: The metting is about to begin.)
be doing 表按计划即将发生的动作,用进行时形式表将来时间,但只适用于表位置移动的动词,go come leave,ect. 并常伴有表将来时间的状语以区别进行时。 (eg:Where are you going this Saturday?)