1、“by＋时间”与动作性强的动词连用时，主句多用于完成式。by后的时间可指现在、过去或将来时间点。
如：By the time he was fourteen year sold，he had learned maths all by himself. I shall have finished it by the time you come back.
By the end of the match, they had kicked two goals and we had kicked four.
They must have finished their work by this time.
但是，上述情况中当时间为将来时，主句动作发生在
从句动作之后时，主句动词可用一般时态。如：If you're not better by then, I'll take you to see the doctor.如果到那时还不好些，我就带你去看病。
Can you finish this by tomorrow? 在明天以前你能做完这件事吗？
间或有用进行式的。如：By the end of the first week the head of the department was saying very nice things about me. 第一周末时系主任给我多多美言了几句。
2、“by+时间”与表状态的动词连用多用于一般式。by后时间可为现在、过去或将来时。如：By the end of the century the population numbered about four million. 到世纪末人口已经达到四百万左右。You can borrow my camera, but I must have it back by five o'clock.我的照像机你可以借去用，但是五点以前一定要还我。
By the time that the security guards had realized what was happening, the gang were already inside the bank. 等到保卫人员明白过来发生了什么事时，那一伙强盗已经进了银行。
He ought to be here by this time /by now.他此刻（现在）应该已经来到这里了。
如强调某状态在某时间前已经完成，也常用完成式。如：By next Sunday you will have stayed with us for three months.至下星期日为止，你将与我们相聚三个月了。
3、“by＋时间”与
祈使句连用，用于一般式。如：Please finish the task by the end of the month.请在月底前完成这项任务。Be here by this time tomorrow.明天这个时候要到这儿。
4、如强调某状态或动作在某时间为止还要继续下去，还可用完成进行式。如：By the time you graduate,I shall have been working here for five years. 到了你毕业时，我就在此地一直工作了五年之久