as soon as 的'用法一般是两种情况：
1、指未发生的动作,规律是：主句一般将来时,从句用一般现在时代替一般将来时
如：I will tell him the news as soon as he comes back.
注：有时,为了特意表达刚刚完成某事就如何如何,需要用现在完成时.
如：I will go with you as soon as I have washed my face.
2、指紧接着发生的两个短动作,主从句都用一般过去时
如 He took out his English books as soon as he sat down
不过,我也见过从句和主句都用一般现在时的情况.
如：As soon as he finishes his classwork,he runs out of the class.他一做完课堂作业,就跑出了教室.
总之,记住那两种基本的情况,不把时态用得太混乱了就行了（比如后面从句里用了将来时,就绝对允许了）.
