as soon as 的用法一般是兩種情況：
1、指未發生的動作,規律是：主句一般將來時,從句用一般現在時代替一般將來時
如：I will tell him the news as soon as he comes back.
注：有時,為了特意表達剛剛完成某事就如何如何,需要用現在完成時.
如：I will go with you as soon as I have washed my face.
2、指緊接著發生的兩個短動作,主從句都用一般過去時
如 He took out his English books as soon as he sat down
不過,我也見過從句和主句都用一般現在時的情況.
如：As soon as he finishes his classwork,he runs out of the class.他一做完課堂作業,就跑出了教室.
總之,記住那兩種基本的情況,不把時態用得太混亂了就行了（比如后面從句里用了將來時,就絕對允許了）.