区别是: It's very kind of you是正确用法, 而It's very kind for you是错误用法。
只有 be kind to 和 be kind of 的用法, 后面加for是错误的。
kind作表语时，如果主语是人，有两种结构：
1、be kind of
基本句式: sb. is kind to do sth.
句式变形, 用it作主语: It is kind of sb. to do sth.
不定式可省略：It is kind of sb.
例如：
You are kind to help me.
It is kind of you to help me.
It is kind of you.
这三句话的意思一样，都是“你能帮助我，真是个好人/真是热心人。”
注意这个结构中不定式不是真正主语，而是表语形容词kind的状语（原因或方面）。of不可以用for替换。因为这不是不定式复合结构（即不是带有自己逻辑主语的不定式）。
2、be kind to
sb. is kind。某人很热心/善良/慈悲。
这时，可以后接介词to表示对谁热心/善良/慈悲。
She is very kind (to us).
扩展资料
例句
1、It was very kind of you to come.
你能来真是太好了。
2、It's kind of you to say so.
你这样说真是太善良了。
3、That's great! It's very kind of you!
那好极了！你们真是太好了。
4、Thank you very much. It's so kind of you.
你们太好了；太感谢你们了。
5、It's very kind of you to offer me so much help.
你真好，给我提供了这么多的帮助。