这是一个主语从句,it是形式主语,真正的主语是that后面的从句.
It‘s reported that 据报道.
It's said that 据说.
It's believed that 人们相信.
It's accepted that 被接受.
It's estimated that 据估计.
It's well-known众所周知.
均属于这一类从句