have you ever been to HK和I HAVE been there for 3 years为什么一个有to一个没有

HK表示的是名称,故必须加to,而there 是副词,一定不能加to, 再如:
go home,come here,go there 等等

the difference is
been to HK,到哪去过
be somewhere physically 在那里呆过

因为there 是个副词 前面不加介词
就像home一样 只说go home
不说go to home

have been to表示“曾到过…地方”，而Have been there 是“到过那里”的意思，很多人都容易把它们弄混淆！

there 是副词，所以前面不能加介词to