Wait, isnt aircrack-ng use to decrypt the wifi password?
this bring back memories, Btw, the GPU must be powerfull to execute alot of parallel wifi key attack, it will try every each kind of password combination.
indeed CPU is powerfull, clocked at gigahz, but a gpu just under GHZ but with many core will do better cracking.

anyways, is anyone know how to crack WPA password?
care to teach me?

Yes, in term of speed CPU win,
but in term who can do lot of work at the same time, GPU is the clear winner,

for example.
the Core i7-3970X is 6 core processor- the price tag, i belive it somewhere near rm3k
and ATI HD 7990 is have 64 Compute Units (4096 Stream Processors) and the price is the same as i7.

when you saw the number of processor core,
6 against 4096, its clearly the GPU have the advantage doing parallel work,
not to mention, you could plug in more GPU in a single motherboard to stack the GPU power.