Aluminum doped zinc oxide (AZO) thin films were deposited by the radio frequency magnetron sputtering with double target, used as the low resistance window layers of Cu₂ZnSnS₄ (CZTS) solar cells. The influences of Ar flow on the optic-electronic performances of AZO thin films were investigated with 60W sputtering power and 30 mins sputtering time, such as the crystallinity, surface morphology, transmittance, carrier concentration and resistivity. It is showed that, 22 sccm is the saturated Ar flow. Under this flow, AZO grains are bigger, the crystallinity of films are better, the carrier concentration is higher, while the resistivity is lower. The average transmittance of the AZO film is 87.2% range from 400 nm to 1100 nm wavelength.