两个词起首词性差别。in fear可能做动词跟名词，而afraid是描述词，只作表语。
1、afraid 意思是怕，害怕。它是描述词，平日与to be连用，可能广泛地用以表示害怕心思。
比方：Don't be afraid. 不关键怕。
We are not afraid of difficulties. 我们不怕艰苦。
That is what I was afraid of. 我所怕者就在于此。
I was afraid of hurting his feelings. 我害怕伤他的感情。
He is afraid to jump.他不敢跳。
2、in fear 意思是害怕。它是动词，与be afraid每每可能通用，但不如 be afraid常用（特别是在书面语中）。
比方：we fear no difficulty．我们不怕艰苦。
He feared to speak his mind．他不敢说出本人的主意。
Fearing that he would catch cold， I went out to see him．因为怕他会吃惊，我走去看他。
1、afraid，发音英[əˈfreɪd]；美[əˈfred]，描述词，生怕； 害怕的； 担心的； 害怕，害怕。
例句：She did not seem at all afraid.
2、in fear，发音英 [fɪə(r)] 美 [fɪr] n. 害怕;可能性;（对神等的）敬畏;忧愁 vt. 害怕;害怕;为…忧愁（或担心、焦急）;敬畏（神等）vi. 害怕;害怕;忧愁;感到害怕
例句：I was sitting on the floor shivering with fear.