The invention relates to a carburizing and quenching method of a low-speed heavy-duty gear. The carburizing and quenching method comprises the steps of (1) temperature increase and temperature uniformization; (2) strong carburizing; (3) diffusion; (4) temperature decrease; (5) high-temperature tempering; (6) quenching; (7) cold treatment; and (8) low temperature tempering. According to the carburizing and quenching method of the low-speed heavy-duty gear, harmful carbide of a gear carburized layer can be effectively removed, dispersively distributed fine granular carbide can be obtained, the content of retained austenite on the surface is greatly decreased, a metallographic structure of the gear surface is improved, the surface hardness and abrasion resistance of the gear are improved, and the heat treatment property of a product is improved.