一、A=B.即A与B双方程度相等时,用“as+原级+as”的结构来表示.例如：
Oil produced waste gases almost as harmful as the gases from factories.
Tom runs as fast as Jack.
He is a fellow as tall as his elder brother.（=He is as tall a fellow as his elder brother.）
二、A≠B.即A与B双方程度不等时,则用“not as(so) +原级+as”的结构来表示.例如：
London is not so modern as New York.
Sound does not travel as fast as light.
No one is so blind as the people who will not see.
三、A=nB.即双方相比,A是B的若干倍时,用“倍数+as+原级+as”的结构来表示.例如：
This room is about two-thirds as large as that one.（=This room is about two-thirds the size of that one.）
There are twice as many students in our school as there were in 1949.
四、A>B.即A方超过B方时,要用“比较级+than”的结构来表示.例如：
She is five years older than I.（= She is older than me by 5 years.）
He studies harder than any of the others in his class.
五、An+B.即A方超过B方的程度和数量时,用“much (far)/ three times/ five years etc.+比较级+than”的结构来表示.例如：
He works far better than you.
Ann is much nicer than her sister.