it是形式主語，指代后置的主語從句。如果用正常語序that is said，其實就是 “one says＋that引導的賓語從句” 的被動語態(tài)，未免主語部分太長，顯得結構臃腫，所以就改用 it is said that句式。

it is said that用法

it is said that是據說，據傳言的意思

過去式，it was said that + 句子，【謂語用過去時】

現在時，it is said that +句子【謂語用現在時】

將來時，it will be said that +句子【謂語用將來時】

例句：

Someone says that she( works) as an actress.

It is said that she works as an actress.

She is said to work as an actress.