by the time的用法：

　　1、到…時(shí)候?yàn)橹梗?/p>

　　表示到...為止,一般要求主句用過去完成時(shí).

　　例句：

　　He had left by the time we reached home.

　　當(dāng)我們到家的時(shí)候他已經(jīng)走了.

　　The movie had begun by the time we got there.

　　當(dāng)我們到那兒的時(shí)候,電影已經(jīng)開始了.

　　2、到……的時(shí)候：

　　(1)可以表示將來的時(shí)間. 主句用將來完成時(shí),而從句用一般現(xiàn)在時(shí)來表示將來的動作.

　　I will have finished the work by the time my father comes back.

　　(2)可以表示過去的時(shí)間. 主句用過去完成時(shí),而從句用一般過去時(shí).

　　He had built a lab for himself by the time he was 12 years old.

　　注：如果只是說過去某個(gè)時(shí)候的狀況，用過去時(shí)，而不用完成時(shí)。

　　例句： By the time the war was over , death and suffering were to be seen everywhere.

　　在戰(zhàn)爭結(jié)束的時(shí)候，到處可見死亡和饑餓。

　　這里沒有“死亡和饑餓”已經(jīng)完成的意思，只是描述當(dāng)時(shí)這個(gè)時(shí)間點(diǎn)的狀況。所以用過去時(shí)。