过去分词表示已经完成或被动意义。be+过去分词构成被动语态,have+过去分词构成现在完成时,had+过去分词构成过去完成时。例如:This desk is made of wood.这个桌子是木头造的。(被动语态)I have been to Beijing two times.我去过北京两次。(现在完成时)The train had gone when we arrived.当我们到时,火车已经开走了。(过去完成时)The book written by him is very popular.他写的书很受欢迎。(表示被动)