The invention relates to an overlaying process for high-medium pressure rotor thrust disk made of ultra supercritical 12% Cr steel, relating to an overlaying method for a rotor trust disk and aiming to solve problems that the adhering sintering generated between the rotor thrust disk and a bearing bush causes the abnormal condition of the shafts and endangers the safe running of the rotor, even the unit. The overlaying process comprises the following steps of: firstly, processing a first end surface to be overlaid, a second end surface to be overlaid and a shaft neck before welding; secondly, carrying out the dyeing inspection on the processing surface; thirdly, assembling the rotor to a rotating device of a special overlaying device; fourthly, preheating the processing surface; fifthly, overlaying the first end surface to be overlaid and the second end surface to be overlaid; sixthly, de-stressing and thermally processing the first overlaying surface and the second overlaying surface; seventhly, turning and finely processing the first overlaying surface, the second overlaying surface, the shaft neck, the outer surface of the first thrust disk and the outer surface of the second thrust disk after the overlaying operation; and eighthly, carrying out the non-destructive inspection to the first overlaying surface and the second overlaying surface. The invention is applied to overlaying the high-medium pressure rotor thrust disk made of ultra supercritical 12% Cr steel.