have的过去式和过去分词都是had,但是具体应用有区别.
1.表示过去用过去式：We had a meeting yesterday .(发生在过去)
2.表示现在完成（助动词的现在式+过去分词）：We have had a meeting just now.(虽然发生在过去,却对现在产生了影响,即会议的进程在说话时依然清晰可见)
3.表示过去完成（助动词的过去式+过去分词）：We told him we had had a meeting the day before yesterday.（发生在told的过去,即过去的过去）