The invention discloses a method for manufacturing high-quality SCr420 HB automobile gear steel. The method aims at reducing the oxygen content and occluded foreign substances in the steel, guaranteeing the stability of the quenching degree and guaranteeing the high quality of the surface of the steel. The method includes the process routes of using an ultra high power electric furnace, conducting LF, conducting VD, conducting continuous casting, continuously heating through the ultra high power electric furnace, conducting rolling through a continuous rolling mill, conducting finishing, conducting straightening and chamfering, conducting surface eddy current testing and packaging. The continuous casting in the steelmaking process adopts long nozzle protection, casting powder and argon shielding pouring, internal control compositions are appropriately designed, the N element content in the steel is controlled, and the form of the B element in the steel is controlled. The superheat degree and the casting speed in the continuous casting are controlled. The method has the advantages of reducing the oxygen content and the occluded foreign substances in the steel, enabling the gas oxygen content in the steel to be less than 15ppm, and enabling the non-metallic inclusion completely to meet the Korea modern standards, controlling the close limit of the chemical element, guaranteeing the quenching degree, guaranteeing the high quality of the surface of the steel, and meeting the precision forging requirement.