Question

Don't be afraid 为什么要加be

Answer 1

afraid是形容词不是动词，句中作表语，需要在前连接系动词be构成系表结构

afraid 形容词 a.
害怕的,怕的[(+of)][+to-v][+(that)]
She was afraid that she might lose her job.
她担心会丢掉工作。
2.(用于提出异议,告诉不好的消息等场合,使语气婉转)恐怕,遗憾[+(that)]
I'm afraid I can't help you.
对不起,我不能帮你。