When something ISN’T AS GOOD (PRETTY, FAST..) AS something else, we use 没有 /méiyǒu/ instead of 比 /bǐ/
This isn’t as good as that.
这个 没有 那个 好。
Chinese isn't as difficult as Japanese.
汉语 没有 日语 难。
America isn't as big as China.
美国 没有 中国 大。
Their relationship isn't as good as before.
他们 的 关系 没有 以前 好。
Chinese food isn’t as good as Japanese food.
中国菜 没有 日本菜 好吃。
My Chinese isn't as good as his.
我的 中文 没有 他 (的) 好。
Beijing isn't as safe as you think.
北京 没有 你 想 得 那么 安全。
Her hair isn't as long as before.
她的 头发 没有 以前 长。