On the basis of the traditional M-B model,a three-dimensional fractal model of normal contact stiffness of joint surface is constructed by taking into account the elastic-plastic deformation of micro-bulge and by using the modified W-M function which can better describe the actual surface topography of joint surface.Then,the influences of the fractal scale parameters and the fractal dimension on the normal contact stiffness are investigated through the constructed model,and some phenomena are analyzed.The results show that ( 1) the normal stiffness of joint surface increases with the normal load and the material parameters σy /E ,while it decreases with the increase of the fractal scale parameters; ( 2) with the increase of the fractal dimension,the normal stiffness of joint surface increases when 2. 1≤ D ≤2. 6 but it decreases when 2. 6≤ D ≤2. 9; and ( 3) the normal contact stiffness of the constructed three-dimensional fractal model is less than that of the two-dimensional fractal model with the elastic-plastic deformation.