Although the contact analysis of rough surface is widely used,the corresponding contact mechanism is still unclear.In order to solve this problem,a contact model of two rough surfaces under combined compression-shear lcad is proposed. In this model.the Weibull distribution function is introduced to describe the combined roughness of asperity contact,and a shifted spherical harmonics expansion is employed to describe the contact orien-tation probability distribution.Analytical results show that roughness greatly affects the normal and shear stiffness,and that the asperity contact orientation,which is an important parameter of the model,also remarkably affects the shear stiffness.The analytical results accord well with the experimental ones,which means that the proposed model is of high effectiveness.