Abstract: The effect of contact area on wear is not clear at present. Wear tests of brass pins of different sizes sliding against 40Cr discs were investigated at fixed loads and pressures. Results indicated that the wear rates first became smaller and then tended to be stable as the pin diameter got larger at fixed loads. A mathematic model was built and can be used to design the geometry of frictional pair and predict its lifetime. The wear rate first got smaller and then tended to be stable as the diameter of pin increased at fixed pressure. Finally, the roles of the heat generation and heat dissipation of the pin on above results were discussed.