Aiming at the poor meshing state of helical cylindrical gears with changing center distance in high-speed rolling mills, considering gear meshing misalignment, a finite element meshing model of gears has been established in Abaqus. Under typical working condition, the simulation analysis of gear tooth contact has been carried out to study the influence law of center distance change on gear meshing performance parameters. And on this basis, the tooth surface has been optimized for comprehensive modifications including linear reliefs and crowning reliefs in the direction of tooth lead, tip reliefs in the direction of tooth profile. Then , the meshing performance of the gears before and after modification has been comparatively analyzed. The results show that , before tooth surface modifications, the tooth surface bias load phenomenon is serious, and the increase of the center distance makes the contact ratio and the percentage of contact pattern decrease to a large extent, and the maximum contact stress, the maximum root bending stress and the peak-to-peak value of the transmission error increase a lot, the overall meshing performance of the gear decrease obviously in short; After the optimization of modifications, the tooth surface bias load phenomenon is well improved, the maximum contact stress, the maximum bending stress and the peak-to-peak value of transmission error are significantly reduced, the gear mesh condition is well improved and the ability to compensate for changes in the center distance of the tooth surfaces is increased.