as引导的定语从句用法如下：

①as引导的限制性定语从句：as可引导限制性定语从句，用于指代与先行词同类型的人或物，在从句中作主语、宾语或表语。常与such, same等连用。

②as引导的非限定性定语从句as可引导非限制性定语从句，含有“正如/像”之意。

1.常用于指代整个主句，对主句内容进行评述或加以说明，有点像插入语。在从句中作主语、宾语或表语

2.as引导的非限制性定语从句，可在主句前或后，常与 know, say, explain, mention, expect, see等搭配。3.as有时可指代主句中的名词，作主语补语。常见句型搭配：

As is often the case 通常如此

As is well known to all 众所周知

As has been said/stated above/before 如上所述

As was expected 正如预料的那样

As has been pointed out 业已指出

As explained before 如前所释

As has been proved 业已证明

As might be expected 正如所料

As mentioned above 如上所述

As often happens 正如经常发生的那样

As is shown in the picture 如图中所示

As has been announced 正如被宣布的那样

As often happens 正如经常发生的那样

As appears 正如呈现的那样

As we all know 正如我们所知

As we can see 正如我们所见

As we had expected 正如我们所料