This paper establishes a time-varying meshing stiffness (TVMS) analytical model for asymmetric gear pair based on the potential energy principle to analyze the TVMS, transmission error, and load share ratio of asymmetric gears. The model considers the adjacent teeth' influence on the body deformation of the gear teeth and is verified the reasonableness by finite element analysis. The effect of tooth tip relief on the characteristics of asymmetric gear pairs is analyzed in this paper. Considering the tooth profile deviation due to tip relief and tooth profile error of the asymmetric gear can obtain results that are closer to the original meshing condition. The results show that the gear contact ratio decreases with the increase of one side of the gear pressure angle. Conversely, the TVMS of spur gear will increase in a certain extent. During modification section of tooth profile, some significant variations will happen on the behaviors of asymmetric gears such as TVMS, transmission error and load share ratio. Slight tooth profile errors on the surface produce conspicuous fluctuations in gear meshing characteristics.