Paper-based friction material reinforced by carbon fiber is a new type wet friction material for automobile transmission. Based on the same percentage of components, paper-based friction materials reinforced by carbon fiber with different porosity percentage were prepared by changing the thickness of friction materials. The porosity percentage of materials was obtained
by a liquid permeation method. The surfaces of samples were analyzed by using scanning electronic microscope (SEM). The effects of porosity percentage on wet friction performance were investigated by using an inertia friction tester machine. Experiment results show that short carbon fiber is dispersed in resin matrix uniformly, as a result, pores with different sizes are formed inthis way. With the increase of porosity percentage, the shape of friction torque curves becomes flat, and the dynamic friction coefficient tends to increase in the procession, but the trend of static friction coefficient is reversed, the wear rate is trending up.