So when i was 6th dan my belt rank was 21 now when i am 7th dan my rank uped to 336 dafuq?

To my understanding there might be more 7th dans versus people that are 6th dan. So you would have to do the ranking again.

If you see a white belt and their rank is like '2582313' it's because there are a lot of white belts. If you were... say god belt, you wouldn't be ranked that low since the lack of people in that belt.

I think my rank belt uped just because it depends on your belt, so i think i will need to fight again for my belt rank. :|

Yep, kinda what I said. :P

Global rank is global.

Mod rank is for a mod.

There is no belt rank, you just lost more at 7th dan than 6th (or farmed less)

There is a belt rank, it's a part of the old system and it tells you who's closest to the next belt.
Global rank is the new rank system and has nothing to do with belt.
Mod rank is like global rank but for a certain mod.

Correct me if i'm wrong, i don't know much about the ranking system, but i do know there is a belt rank.

I already knew that but, i was confused about that my belt rank uped from 21 to 336 dafuq?

Well, its pretty easy:

Your belt rank gets better, the more often you play games and get qi. Because the belt rank tells you, who of your belt is the closest to get the higher belt. So if you have 7999 games played, you might be belt rank 1, because you are the closest player to the 8th Dan.

So if you get a new belt, and you have 8000 games played, you have the last place on the belt rank, because you are 1000 games away to get the higher belt.

sry 4 bad english