by then用将来完成时。例句：Be married next Christmas, for you will have got your master's degree by then.明年圣诞结婚吧，因为到那时你已经拿到硕士学位了。
双语例句
1、By then, it was October and we were more than halfway through our tour.
那时已是10月，我们已经完成了行程的一大半了。
2、We all knew by then that the affair was practically over.
到那时，我们都知道事情实际上已经结束了。
3、It had been supposed that by then Peter would be married.
人们一直认为到那时彼得应该结婚了。
4、At this rate, she would be almost seven feet tall by then
这样下去，她到时将有7英尺高了。
5、The doctor said it will take six weeks and I should be fine by then
医生说需要6周时间，到那时我就会好了。