1、词性不同

because 是连词，其后接句子；because of 是复合介词，其后接名词、代词、动名词、what 从句等。如：

I didn’t buy it because it was too expensive. 我没有买是因为它太贵了。

He is here because of you (that). 他为你(那事)而来这里。

2、搭配不同

because 所引导的从句除用作原因状语外，还可用作表语。而复合介词 because of 所引导的介词短语通常用作状语而不用作表语。

It is because he loves you. 那是因为他爱你。

His absence was due to the rain.