“it +be +过去分词+从句” 结构

你说的“it +be +过去分词+从句”是主语从句.
原先,是由宾语从句变来的:
They say that he enjoys classic music(宾语从句)-----------（主语从句）：It is said that he enjoys classic music.
分析：It （形式主语）is said（谓语） that （主语从句引导词）he enjoys classic music.(真正主语)
以下是常用的相同句型：
It is said / reported / supposed / thought / believed / estimated / known / found / considered / announced + that + 句子.
千万注意：told 不属于这个句型--------It is told (told必须改换成said) that he will come tomorrow.

1. It is said (reported, learned…) that …
该句型中的it 仍是形式主语，真正主语是 that 引导的主语从句。该结构常译为“ 据说（据报道，据悉……）”。
It is said that he has come to Beijing. 　　
It is reported that another man-made satellit...