Photoluminescence(PL) of Gallium nitride (GaN) films grown by ammoniating Ga2O3/Al2O3 films deposited on silicon (111) by rf magnetron sputtering has been studied. The mechanism and the influence of growth condition on the photoluminescence is also studied. There are two emission peaks: a strong one at 347 nm, and a weak one at 412 nm. Increasing the ammoniating temperature and lengthening the ammoniating time, the intensities of both two peaks increase, but the in locations do not move. The peak at 347 nm is considered to be the blue-shift, which was caused by micro- size of GaN grains, of the band-edge emission peak of GaN. The emission peak at 412 nm is attributed to radiant combination from conduct band to the energy level of acceptor impurity.