have no idea 是英语中得固定搭配.idea 是思想、观念、意见的意思,比较抽象,实际上在这个短语中,它整个词组的意思就是“不知道”,表示一点想法也没有
例句与用法：
I have no idea why he resigned his post.我不知道他为何辞去他的职务.
I have no idea (as to) what you mean.我一点儿也不明白你的意思.
We have no idea how to persuade him to give up the idea.我们不知道如何说服他放弃这个念头.
I have no idea what to do.我不知道该怎么办.
We have no idea how the birds find their way.我们不知道这些鸟如何找到它们的路.
You have no idea how worried I was.你想像不出来我有多么担心.