Due to the friction moment, when two flat rough surfaces come to sliding contact or quasi-sliding contact, there is an inclined angle between these two surfaces. A two degree-of-freedom inclined rough surface contact model is presented in this work and the effects of the angular displacement on the friction coefficient, interfacial forces, and interfacial moments for the elastic-plastic planar rough surfaces contact are investigated. The numerical simulations show that both interfacial forces and interfacial moments gain with the increase of the inclined angle while the friction coefficient decreases instead. In addition, for a given sliding mass block system, the effects of that friction coefficient and base sliding speed on the stability of the sliding contact are also discussed. The simulations indicate that a larger friction coefficient and a higher base sliding speed tend to turn over the mass block during the sliding.