英语短语"not as…as"是同级比较的否定形式，核心含义是：“不如……；不像……一样（具有某种特征/程度）”。它用于对比两个事物/人的同一属性，说明前者在该属性上的程度低于后者。
"not as…as"的完整结构为：
注意：
比较的是同一类属性（如身高、速度、价格等）；
形容词/副词必须用原级（不能用比较级或最高级）；
比较对象要前后一致（避免偷换概念，如用代词代替重复的名词）。
根据修饰的词类（形容词/副词/名词），"not as…as"的用法可细分为以下几类：
用于对比人/物的状态、性质或外貌等，结构为：
例：
He is not as tall as his father.（他不如他父亲高。）
This dress is not as beautiful as that one.（这条裙子不如那条漂亮。）
The weather today is not as hot as yesterday.（今天的天气不如昨天热。）
用于对比动作的方式、速度、频率等，结构为：
主语 + 实义动词 + not as + 副词 + as + 比较对象（需借助助动词do/does/did）例：
She doesn’t run as fast as me.（她跑得不如我快。）
He didn’t speak as clearly as his teacher.（他说话不如他老师清楚。）
They don’t work as hard as we do.（他们工作不如我们努力。）
当比较的是“具有某种特征的人/物”时，结构为：
例：
He is not as good a student as his sister.（他不如他姐姐是个好学生。）
This is not as interesting a book as that one.（这本书不如那本有趣。）
在"not as…as"中间加入nearly（几乎不），表示“远不如；根本不如”，加强否定程度。
例：
This restaurant is not nearly as good as the one we went to last week.（这家餐厅远不如我们上周去的那家好。）
She is not nearly as rich as her cousin.（她根本不如她表妹有钱。）
当主句是“I don’t think/believe/suppose…”时，否定会转移到宾语从句，表示“我认为……不如……”。
例：
I don’t think he is as smart as you.（我认为他不如你聪明。）
She doesn’t believe the movie is as exciting as the book.（她认为这部电影不如书精彩。）
"not as…as"可与less + 形容词/副词原级 + than互换（前者更口语，后者更正式）。
例：
He is not as tall as his father. = He is less tall than his father.（他不如父亲高。）
This dress is not as beautiful as that one. = This dress is less beautiful than that one.（这条裙子不如那条漂亮。）
1、 不能用比较级："as…as"和"not as…as"中间必须用原级，不能用比较级（如taller/faster）。
❌ 错误：He is not as taller as me.
✅ 正确：He is not as tall as me.
2、 比较对象要一致：避免前后对比的事物不同类（如用“我的自行车”和“你的汽车”比速度，需用代词代替重复的名词）。
❌ 错误：My bike is not as fast as your car.（逻辑可接受，但更简洁的表达是：My bike is not as fast as yours.）
✅ 正确：My bike is not as fast as yours.（yours = your bike）
"not as…as"是英语中最常用的否定同级比较结构，核心是“前者不如后者”。只要记住“原级+比较对象一致”的规则，就能轻松使用啦！
再试几个句子巩固：
这个苹果不如那个甜。This apple is not as sweet as that one.
他英语说得不如你流利。He doesn’t speak English as fluently as you.
我认为这部剧不如去年的好看。I don’t think this show is as good as last year’s.