when i download something my bsnl3g speed is very good but when i download on torrent it is only 12kbps if anyone know what is the reason please post it...........

It can be many things.

Have you tested speed of your connection, what is average speed you get ?
you can try site like mobilespeedtest.com

Also, try downloading torrent like Linux OS , may Mint Linux , they have generally lots of seeders, see if it is also giving slow speed or not ?