When something ISN’T AS GOOD (PRETTY, FAST..) AS something else, we use 没有 /méiyǒu/ instead of 比 /bǐ/
EXAMPLES
This isn’t as good as that.
这个 没有 那个 好。
Zhège méiyǒu nàge hǎo.
Chinese isn't as difficult as Japanese.
America isn't as big as China.
美国 没有 中国 大。
<Měiguó méiyǒu Zhōngguó dà.>
My Chinese isn't as good as his.
我的 中文 没有 他 (的) 好。
<Wǒde Zhōngwén méiyǒu tā hǎo.>
Her hair isn't as long as before.
Their relationship isn't as good as before.
Beijing isn't as safe as you think.
My Chinese isn't as fluent as his.