The dynamic characteristic of joint surfaces is of great significance for evaluating the performance of machine tools. In this paper，a normal contact stiffness and damping model of joint surfaces are proposed for studying the complicated contact characteristics of fixed joint surfaces in mixed lubrication. Firstly，the three-dimensional Weierstrass-Mandelbrot function is used to describe the rough surface，and the solid contact stiffness and damping model is established based on the fractal theory. Then，the contact stiffness and damping model of the lubricant are established based on the mean flow generalized Reynolds equation，in which the lubricant contact stiffness is a function of the solid contact stiffness. Finally，the contact stiffness and damping of the solid part，lubricant part and the joint surfaces are analyzed. The results show that the damping of the lubricant film is much larger than that of the solid part，and the contact damping of joint surfaces is mainly dominated by the damping of the lubricant film. The contact stiffness of joint surfaces is dominated by the lubricant contact stiffness in the early stage of contact. However，the ratio of the lubricant contact stiffness to the stiffness of joint surfaces decreases with increasing the real contact area. At last，the solid contact stiffness dominates joint surfaces.