The GaN thin films were grown on Si(111) substrate by Mg-doping simultaneously using a pulsed laser two-beam deposition system. The characteristics of an undepoed GaN film and the Mg-doped GaN film were investigated by using X-ray diffraction, atomic force microscopy, room temperature Van der Pauw-Hall measurements and photoluminescence. It was found that the Mg-doped GaN films have the hexagonal wurtzite crystalline structures similar to the undoped GaN films. As increasing the doped Mg-doped dose, a decrease in the size of grains of the GaN films can be seen, and the GaN films become p-type conductivity. The optical property of Mg-doped GaN film can be improved with increasing p-type carrier concentration. But the p-type carrier concentration can be decrased and the crystalline quality of the GaN films can be degraded by the too high doping Mg dose. The intensity of the yellow band emission peaks become stronger with increasing the doping Mg dose. These results show that it is possible to obtain high p-type carrier concentration in GaN films using the optimal pulsed laser two-beam deposition parameters.