Abstract: The spur gear with an asymmetric involute is a new kind of gear. Its bending stress could not be calculated by existing analytical methods. Through analyzing the tooth profile characteristics, a solving method of bending stress for the gear was proposed on the basis of the plane cross-section method, and an analytical formula was derived to calculate the root bending stress of tile gear. Spur gears with symmetric and asymmetric involutes, with the same module and teeth numbers, were as the research objects. In the same working conditions, the bending strengths of the two gears were studied by the analytical method and finite element method during forward and reverse rotation. Five special positions were selected during the meshing period and their bending stresses on both sides were analyzed comparatively. Finally, by the ladder loading fatigue test method, the two gears were tested in tooth root bending fatigue strength experiment. The experimental data verified the theoretical analysis result.