1. be afraid to do sth… 不敢(害怕)去做某事; 

2. be afraid of doing 担心某事会发生

—比如这样的语境：不敢与顾客吵架, 担心会失去他们，分别用1, 2没问题

3. be afraid of sth.害怕某事(如狗)

[题] Not having come in time, he was afraid ____ scolded.

答：可用of being / that he would be; 不能用to be

be afraid of 与 be afraid to在主语发出动作时才可以互换，

注意后者要有主动性，故意性.

He was afraid of swimming in deep water / he was afraid to swim in deep water.

I was afraid to go near the dog because I was afraid of being bitten (不能用 "afraid to be bitten")

其它2个区别：

He is afraid of falling off a cliff.（一般情况）;

He was afraid to climb that cliff. （某次具体的事）

Don't be afraid to shout if you see him. (去做某事).

Don't be afraid of shouting if you see him. (已经在做的事).