The invention provides a heat treatment process of gear steel for an automobile gearbox. The heat treatment process comprises the steps of normalizing, coarse semi-finished cutting processing, carburizing, quenching, low temperature tempering, shot blasting and processing inspection; in the carburizing process, preheating and pre-carburizing processes are increased to clean impurities, oil stainsand the like attached to the surface of a billet, so that the internal temperature and external temperature of the billet is the consistent, a basis is laid for further temperature rise, heating timeis shortened, and energy consumption is reduced; the temperature and carburizing time in the carburizing process are controlled to obtain flat carbon concentration distribution, stress caused by carburizing heat treatment is reduced, and the mechanical property and wear-resisting property of the surface of the billet are effectively improved; and meanwhile, the billet ingredients, the heating temperature, heat preservation time, cooling speed and other process parameters are controlled, the billet is subjected to carbon potential rising and falling treatment, the process of normalizing, quenching and tempering is optimized, a production cycle is shortened, the energy consumption and production cost are reduced, and the heat treatment process is suitable for producing the gear steel for automobile gearboxes with various specifications.