A method for tuning the work function of a metal gate of the PMOS device is disclosed. The method comprises depositing a layer of metal nitride or a metal on a layer of high-k gate dielectric by physical vapor deposition (PVD), as a metal gate; doping the metal gate with dopants such as Al, Pt, Ru, Ga, Ir by ion implantation; and driving the doped metal ions to the interface between the high-k gate dielectric and interfacial SiO2 by high-temperature annealing so that the doped metal ions accumulate at the interface or generate dipoles by interfacial reaction, which in turn tunes the work function of the metal gate. The method can be widely used and its process is simple and convenient, has a better ability of tuning the work function of the metal gate, and is compatible with the conventional CMOS process.