Mg ions were implanted on Mg-doped GaN grown by metalorganic chemical vapor deposition(MOCVD). The p-type GaN was achieved with high hole concentration(8.28×10¹⁷cm^-3)conformed by Van der pauw Hall measurement after annealing at 800℃ for 1h. This is the first experimental report of Mg implantation on Mg-doped GaN and achieving p-type GaN with high surface hole concentration.