其基本意思为“与…一样”，其中的第一个as为副词，其后通常接形容词或副词(用原级)，第二个as可用作介词(后接名词或代词)或连词(后接从句)。
使用时应注意以下几点。
如：
(1) 在否定句中，第一个as 也可换成so。
如：
He doesn’t study as [so] hard as his brother. 他学习不如他弟弟努力。
(2) 在该结构的两个as之间通常接形容词或副词的原级，但若涉及数量或程度，可用“as much+不可数名词+as”和“as many+复数名词+as”。
如：
You’ve made as many mistakes as I have. 你犯的错误和我犯的一样多。
I haven’t got as much money as I thought. 我不像原来想像的有那么多钱。
其间接形容词时，有时该形容词还可修饰另一名词，但这个名词应带有不定冠词(注意词序)。
如：
She is as good a teacher as her mother. 她和她妈妈一样是位好老师。
也可说。
如：She is a teacher as good as her mother.
但不说。
如：She is as a good teacher as her mother. / They are as good teachers as us.
(3) 第二个as后接从句时，该as通常为连词，但有时这个as还充当其后从句的主语或宾语，此时该as实为关系代词。
如：
I gave him as much as he could eat. 他能吃多少，我就给了他多少。
We’ve got food for as many people as want it. 我们的食物，无论多少人吃都够了。
(4) 该结构根据情况可用使用以下修饰语。
如：(not) nearly, almost, just, nothing like, exactly, not quite, half, one-ten, twice, three times, 30 per cent等，并且这些修饰语必须置于第一个as之前，而不能置于其后。
如：
He doesn’t play half as well as his sister. 他演奏的水平不及他姐姐的一半。
This dress is twice as expensive as that. 这件连衣裙比那件贵一倍。
(5) 若第二个as引导一个表示将来意义的从句，则该从句可用现在时表示将来，也可直接使用将来时态。
如：
We’ll get there as soon as you do [will]. 你一到，我们就到。
(6) 在非正式场合(尤其是美国英语中)，有时可以省略第一个as。
如：
When over forty, he married a woman poor as himself. 他在40多岁时娶了一个像他本人一样穷的女人。
另外，若意思明确，有时可省略第二个as及其后的相关词语。
如：
The radios in that shop will be cheaper, but not as good. 那家商店的收音机会便宜些，但质量没那么好。
“as + 形容词或副词原级+ as…”意为“和……一样”，表示同级的比较，但要注意第一个as 为副词，第二个as 为连词。
根据比较对象和性质的不同又可以把此种结构分为三种：
（一）“ as … as …结构”用于表示不同人或物同一性质的比较，意为“……和……一样…… " 。
例如The tree is as tall as the building(is) ．
这棵树和那栋楼一样高。
注意此结构也常用于形象比喻中：as cool as cucumber 沉着的，as stubborn as a mule 非常顽强的，倔强的，as clear as crystal 非常透明的，as poor as a church mouse 非常贫困的，as busy as a bee 像蜜蜂一样忙碌，as easy as ABC 像ABC 一样容易，as deep as a well 像井一样深，as light as a feather 像羽毛一样轻，as soft as butter 像黄油一样软。
这些短语生动活泼，浅显易懂，记住这些短语可以提高学生的英语写作和口语能力。
（二）“ as … as …结构”用于表示同一个人或物不同性质的比较，意为“既……又……”。
例如：
This swimming pool is as wide as it is long.
这个游泳池宽度和长度相等。
（三）“ as … as …结构”用于表示两个人或物不同性质的比较，表示程度相同或相当，意为“……而……”。
在否定句中结构是“ so/as…as…”。
例如：
He was as handsome as his wife was beautiful ．
他长得非常英俊，他的妻子也长得非常漂亮。
He was as experienced as his brother was green ．
他经验丰富，而他兄弟却涉世未深。
He cannot run so/as fast as you.
他没你跑得快。
Danny is not so/as wise as he is witty ．
丹尼为人风趣，但欠明智。
需要注意的是：“as + 形容词或副词原级+ as…”结构的变体形式是“ as + 形容词+ a + 单数名词+ as 或as + many/much + 名词+ as ”。
意为“……和……一样…… " 。
例如：
I don't want as expensive a car as this. ＝I don't want a car as expensive as this ．
我不要这么贵的汽车。
This is as good an example as the other is.
这个例子和另外一个例子一样好。
Tony is as clever a boy as his brother ．。