when i was feeding my gf,one of em was trying to compete food and accidently swallowed a stone, i watched him like 30mins, still stuck in here.... will it kill my godlfish????

Can you still see it in his mouth?
If you can, you need to try and get it out or it could kill him yes.
Hold him slightly out of the water and use a round-edge pair of tweezers to try and ease the stone out, being careful not to do any damage to his mouth.

If you cant see it, are you sure its still in there?
..I dont think they can actually swallow-swallow them, not sure they would fit.. how big was it?

the tiny stone, i think its also the same size of the hikari lionhead pellet.i didnt c the stone come out.will the stone ran through his disgestiive system?

oh ya, its a baby bf...

I've no idea if it will pass through him..
If its really small it might. But if you can still see it and think you can get at it, then his best chances are if you can get it out without hurting him.