兩者用法的區別如下

1、詞性不同

because 是連詞，其後接句子；because of 是複合介詞，其後接名詞、代詞、動名詞、what 從句等。如：

I didn’t buy it because it was too expensive. 我沒有買是因爲它太貴了。

He is here because of you (that). 他爲你(那事)而來這裏。

2、搭配不同

because 所引導的從句除用作原因狀語外，還可用作表語。而複合介詞 because of 所引導的介詞短語通常用作狀語而不用作表語。

It is because he loves you. 那是因爲他愛你。

His absence was due to the rain.