回複：Can TN visa directly change to Green card ?

(1) yes
(2) don't think there is such prerequisite
(3) it's a long journey(check priority date), if you were born in mainland china.
this topic has been discussed a lot all over the internet. you can search them to get an idea. basically it is doable, however it might get tricky when it comes to TN renewal. check with your lawyer/look through internet, you can find lots of resources.