“as…as” 是一个常见的英语比较结构，主要有以下含义和用法：
一、用于同等程度的比较
“as + 形容词 / 副词原级 + as” 表示 “和…… 一样……”
例如：“This tree is as tall as that one.”（这棵树和那棵树一样高。）其中 “tall” 是形容词原级，用于比较两棵树的高度。
又如：“He can run as fast as his father.”（他能跑得和他父亲一样快。）“fast” 是副词原级，比较两人跑步的速度。
否定形式为 “not as/so + 形容词 / 副词原级 + as”，意思是 “不如……”
例如：“This book is not as interesting as that one.”（这本书不如那本书有趣。）
再如：“She doesn't sing as well as her sister.”（她唱歌不如她姐姐唱得好。）
二、特殊用法
“as many/much as...”
“as many as + 可数名词复数” 表示 “多达……（可数）”，例如：“There are as many as 50 students in this class.”（这个班的学生多达 50 人。）
“as much as + 不可数名词” 表示 “多达……（不可数）”，例如：“He drank as much as 2 liters of water after the exercise.”（运动后他喝了多达 2 升的水。）
“as...as possible/one can” 表示 “尽可能……”
例如：“Please come as early as possible.”（请尽可能早来。）
或者 “Please come as early as you can.”（请你尽可能早来。）这两种表达意思相近。