它和 as is known to all 是相同的意思,都是“众所周知”,而用法上面略有些不同,as is known to all 只可以用在句首或句尾,用“,”隔开.而as it is known to all不仅可以放在句首,还可以后面加“that”从句.而it is known to all 是形式主语的典型,只用于如it is known to all that our teacher is beauful.