A conceptual constitution of general wear simulation is discussed fundamentally, and a wear simulation system for trapezoid leadscrew is constituted. Conditions which rule wear phenomenon are classified into inside conditions, mechanical conditions and outside conditions. And a wear process is considered as a system which transforms such conditions into evaluation variables of wear. The wear simulation with geometrically simplified models reproduces the local phenomenon of the practical system, and it was assumed that a wear phenomenon is determined by local conditions. Considering the similarity rule on a wear process, it becomes obvious that the contact area ratio and all the local conditions of the simulation model needs to remain identical with those of the practical system. On the basis of these considerations, a wear simulation system for trapezoid leadscrew using cylindrical model is constituted conceptually, and procedure of simulation is given.