A elastic plane strain finite element model of wheel-rail system was established using the finite element analysis software ANSYS to simulate the sliding contact behavior of wheel-rail in the working condition. The effect of sliding speed on the contact stress of the rail contact surface in the condition of mechanical loading, and the effect of sliding speed on the frictional temperature rise and contact stress in the condition of thermal-mechanical coupled load were investigated. The contact stress calculated under these two conditions was compared. Results show that the contact stress gets a significant increase and the distribution is more concentrated on the vicinity of the contact areas in the coupled load conditions compared with the mechanical load conditions, which means the significant friction thermal effect is generated by the relative sliding between wheel-rail. With the increasing of sliding speed, the friction thermal effect is more obvious, and the depth of the heat-affected layers becomes shallower, which means sliding speed has a significant influence on the contact stress, and the impact of sliding speed on the contact stress should be taken into consideration when investigating the contact stress of rail.