anyone can teach me camera distance hack?

No, you won't get banned. This hack has been around since a month after dota 2 beta's release, if not from the start. I can't say for certain since I switched from wc3 dota to valve's dota a month after it came out. AFAIK, anything you edit in the client's DLL is exclusively for how the client functions. That being said, if they really wanted to, I think they could check, but that's not a major concern. I don't have the link but I remember reading a post by a Valve employee somewhere on dota2dev forums saying that they are aware of this "exploit" and that's it. They didn't say they had plans to fix or patch it and they most likely won't because if they do, then people who use a multi-monitor setup for playing dota won't be able to anymore.

or since dota 2 reborn is official and very bugyy. you can find match, join game and type in console sv_cheats 1 -> dota_camera_distance 1800
but i believe this will be very soon patched..