1.Year after year = for a number of years; continuously年年地,年复一年地.把 year 换成其他词,就有：week after week; month after month; generation after generation等许多表达法.
例： We used to go to the seaside for a holiday year after year.
过去我们每年都去海边度假.
Some folk songs are passed on generation after generation.
有些民歌被一代接一代地传唱.
2.有一个用法和sth. after sth.很类似,就是sth. by sth.我们通过一个例句来看看它们的区别：
Year by year 一年年地,逐渐地.
My hair is becoming gray Year by year .
我的头发一年比一年白了.