Abstract: Aiming at the fatigue fracture of the first-speed driving helical gear in an automobile gearbox during operation, this paper conducts a parametric optimization study on the gear by means of ANSYS finite element analysis software. The optimization is carried out based on Hertz contact theory, in which the number of teeth of the driving gear is increased from 20 to 22, the helix angle is adjusted from 15° to 18°, and an asymmetric design with 35 mm face width for the pinion and 28 mm face width for the gear is adopted. The variation of contact stress is then verified through simulation. The results show that the maximum contact stress on the gear tooth surface is significantly reduced after optimization, which meets the cyclic working condition requirements of the vehicle.