一、表示伴隨 意為“隨著”。如： As time passed, things seemed to get worse. 隨著時間的推移，情況似乎變得更糟了。 若其後不接從句，而接名詞，則用介詞 with 表示“隨著”。如： With the development of modern agriculture and industry, more and more waste is produced. 隨著現代工農業的發展，汙染越來越嚴重了。
二、表示讓步 意為“雖然”“儘管”，要用於倒裝句（相當於 though，但語氣稍弱）。如： Boy as he was, he behaved like a girl. 他雖然是個男孩，但舉止卻像個女孩。 Much as I like you, I couldn’t live with you. 我儘管很喜歡你，卻不能和你一起生活。 Try as he would [might]，he couldn’t open the door. 他試過多次了，卻仍打不開門。
三、表示時間 意為“當……時候”。如： He dropped the glass as he stood up. 他站起來時，把杯子摔了。 As I was coming here, I met your brother. 我來這裡時碰到了你的弟弟。 注意，as 引導時態狀語從句時，其謂語動詞通常只能是動作動詞，而不能是靜態或狀態動詞。如： 她出生後不久父母雙亡，是由姑母撫養大的。 誤：Her parents died as she was a baby and she was brought up by her aunt. 正：Her parents died when she was a baby and she was brought up by her aunt.
四、表示原因 引導原因狀語從句時，其謂語動詞可以是動作動詞，也可以是狀態動詞。如： As you weren’t there I left a message. 因為你不在那裡，我留了個信兒。
as 用作連詞用法如下：
一、表示伴隨 意為“隨著”。如： As time passed, things seemed to get worse. 隨著時間的推移，情況似乎變得更糟了。 若其後不接從句，而接名詞，則用介詞 with 表示“隨著”。如： With the development of modern agriculture and industry, more and more waste is produced. 隨著現代工農業的發展，汙染越來越嚴重了。
二、表示讓步 意為“雖然”“儘管”，要用於倒裝句（相當於 though，但語氣稍弱）。如： Boy as he was, he behaved like a girl. 他雖然是個男孩，但舉止卻像個女孩。 Much as I like you, I couldn’t live with you. 我儘管很喜歡你，卻不能和你一起生活。 Try as he would [might]，he couldn’t open the door. 他試過多次了，卻仍打不開門。
三、表示時間 意為“當……時候”。如： He dropped the glass as he stood up. 他站起來時，把杯子摔了。 As I was coming here, I met your brother. 我來這裡時碰到了你的弟弟。 注意，as 引導時態狀語從句時，其謂語動詞通常只能是動作動詞，而不能是靜態或狀態動詞。如： 她出生後不久父母雙亡，是由姑母撫養大的。 誤：Her parents died as she was a baby and she was brought up by her aunt. 正：Her parents died when she was a baby and she was brought up by her aunt.
四、表示原因 引導原因狀語從句時，其謂語動詞可以是動作動詞，也可以是狀態動詞。如： As you weren’t there I left a message. 因為你不在那裡，我留了個信兒。