The invention provides a method for improving performances of a high k gate dielectric through interface passivation. The method comprises the steps of depositing an amorphous alumina film and a gadolinium oxide doped hafnium oxide film on a silicon substrate in sequence. According to the method, a specific ceramic post sintering technology is adopted to prepare a high-purity alumina target, the amorphous alumina film layer is deposited on the silicon substrate, and then the gadolinium oxide doped hafnium oxide film is deposited on the alumina film layer. According to the method, since the amorphous alumina film is deposited between the silicon substrate and the gadolinium oxide doped hafnium oxide film, an interface passivation layer is formed between the substrate and a high k gate dielectric layer, interdiffusion of Si, O and Hf atoms is prevented effectively, an Si/Al2O3 interface forms single SiOx, the formation of hafnium silicide or hafnium silicate at the interface is reduced, and charge defects are decreased at the interface and the stability is improved due to dense and stable Al2O3.