Running-in should be regarded as a self-adapting and convergent process of a dynamic system. The effect of surface roughness on dynamic behavior of a lubricated sliding wear system has been explored in this paper. With the RMS σ of a composite roughness considered as the characterizing parameter of the mating surfaces, two state equations: the wear equation concerning the effect of roughness and the rate of equation concerning changes in RMS, have been established. The optimum roughness of a wear system corresponding to the minimum wear rate and the equilibrium roughness produced by the running-in, the stability of the wear system and its critical load capacity can be predicted and simulated by this dynamic model.