The opposite of beautiful or handsome is ugly –but that's a strong word, so most people express this idea using the negative form of one of the positive words, for example: “She's not very attractive”or “He's not so good-looking.”
美丽和帅气的反义词当然是丑陋（ugly）啦——但是这可是一个感情色彩很强烈的单词，所以大多数人一般会用褒义词的否定说法来表达“丑”，比如说：“She's not very attractive”（她不是很有吸引力）或者“He's not so good-looking”（他长得不那么好看）。

Finally, there is the word plain –that describes a person who is ordinary-looking –not especially beautiful/handsome, but not especially ugly either.
最后还有一个单词plain——这个是用来表达一个人相貌平平的，没有特别好看也没有特别丑。