The invention discloses a method for preventing high-K material oxygen diffusion. A metal Ru layer is added and deposited in an interface between an ultra-thin interface layer and the high-k material as a buffering layer; an annealing operation is performed after the high-K material is fully deposited to enable oxygen in the high-K material and the metal Ru to be combined to form stable RuO2, so as to prevent oxygen from reacting with silicon in a substrate to form oxygen diffusion; meanwhile, OH<-> in the ultra-thin interface layer and the high-K material can be prevented from forming sub-oxide HfO2H2x of Hf, so that electrons can be prevented from transferring from Hf to work function metal to form an interface to result in degradation of the effective work function, so that the electrical property and the reliability of a circuit are improved consequently.