在定語從句中，一般的從句關係代詞是which、who、whom、that、 whose, 其代替主句中的人或物，在從句中做主語、賓語或定語。而學生在學習過程中，常會遇到as作爲關係代詞出現，做起題來，無從下手,就此筆者對as作爲關係代詞引導定語從句的情況做一歸納, 以供參考.
一、as引導限制性定語從句
主要結構有：
the same…as
as…as
such…as
so…as
主句中出現the same, as, such, so修飾先行詞，需選擇as做關係代詞在定語從句中做主語或賓語。
1. It’s the same person as we wanted to find yesterday .
我們昨天要找的是同一個人。
2. Such girls as he knows are good at English .
他所認識的女孩都擅長英語。
3. Do you have such books as we like ?
你有我們喜歡那種書嗎？
4. She will marry as healthy a man as she can find .
她將嫁給她能找到的任何一個有錢人。
5. There is so warm a house as we want to live in .
這裏有如此暖和的房子，我們都想住在裏面。
6. He has so difficult a problem , as none of us can solve .
他有如此難的一個問題，我們沒有人能解決。
二、引導非限制性定語從句
⑴ as引導非限制性定語從句，指代整個主句內容，從句可置於句首，句中或句尾
1． As everyone knows ,China is a beautiful country with a long history .
2． The earth , as we know , moves round the sun .
地球，我們都知道，圍着太陽轉。
3． Tom works hard and is willing to help others, as we all know.
湯母工作努力，並且樂於助人，這一點我們都知道。
⑵ 非限制性定語從句中的.謂語爲被動式時，常用as做主語
be said/known/announced/reported/mentioned/expected/discussed
1. Grammar , as has been said before, is not a set of dead rules.
語法，就像以前所說，不是一套死規則。
2. As is known to all , TaiWan is part of China .
⑶ as引導非限制性定語從句，有“如，似，正像”的含義，因此，下列句式多用as
as has been said above
如上所說
as anybody can see
正像每個人所看到的那樣
as we had expected
正如我們所預料的那樣
1. Things are not always as they appear.
事情並不一直像他們表面那樣。
2. The boy has as much progress as we had expected.
正像我們所預料的那樣，這個男孩取得了大的進步。
