不定词和动名词两者都可以，但意思不一样。be afraid to do，不敢，胆怯去做某事，是主观上的原因不去做，意为“怕”；be afraid of doing，担心出现doing的状况、结果。doing是客观上造成的，意为“生怕，恐怕”。
afraid的用法小结
今天我们要学习的是afraid的几个常用词组的用法：
1. be afraid of sth (sb) 害怕某事(某人)。如：
Are you afraid of dogs? 你害狗吗?
There’s nothing to be afraid of. 没什么可害怕的。
比较：
He is afraid of her. 他怕她。
He is afraid with her. 跟她在一起时，他很害怕。
2. be afraid of doing sth
(1) 担心会发生某事或某情况(但实际上未必会发生)。如：
She was afraid of waking her husband. 她怕吵醒她丈夫。
I was afraid of hurting her feelings. 我怕伤害她的感情。
注：be afraid of doing sth 表示担心会发生某事或某情况时，其后也可用 be afraid that 替换。如：
He was afraid of losing face. ＝He was afraid (that) he’d lose face. 他怕失面子。
(2) 害怕做某事或不敢做某事(指缺乏勇气或害怕其后果而不敢)。如：
I’m afraid of telling her. 我不敢告诉她。
He was afraid of jumping. 他不敢跳。
3. be afraid to do sth 害怕做某事或不敢做某事。如：
He was afraid to fly in a plane. 他不敢坐飞机。
He was afraid to go into the house and meet his father. 他不敢进屋去见他父亲。
注：以上两类句型的异同之处：表示担心会发生某事或某情况，只能用 be afraid of doing sth, 而表示害怕做某事或不敢做某事等，则两者都可用。如：
Don’t be afraid to ask [of asking] question. 不要害怕问问题。
He is afraid to go out [of going out] alone at night. 他不敢晚上一个人出去。
