The meshing stiffness of the gear transmission system varies with the surface topography of the gear meshing interface， which directly affects the transmission precision and stability of the gear transmission system. In this paper， an improved time-varying meshing stiffness algorithm is proposed to incorporate the effect of surface topography of the gear mesh interface based on the fractal contact model of the rough surface. In addition， the curved surface contact coefficient is introduced to characterize the influence of tooth meshing curvature and foundation deformation on the distribution function of micro-asperities at the meshing interface. Besides， effects of surface topography， material characteristic and input torque on the time-varying gear meshing stiffness are investigated. The results show that the meshing stiffness reduces with increasing surface roughness， whilst increases with increasing material strength and input torque.