When the train is hauling at high speed or processing emergency brake, the high temperature incurred by friction normally will cause fateful damage to the wheel/rail contact surface, invalidate the wheel/rail and endanger traffic safety. The main factor to cause wear, flatting and checking of the wheel/rail is the friction heat caused by the relative sliding between the wheel and the rail. Focused on this problem, in this article, in order to analyze the temperature rise and thermal stress of the wheel/rail during the wheel's sliding, the author adopted finite element method to perform a thermo-contact coupling calculation on the condition that the wheel is sliding on the rail. The model takes into accounts the impact of wheel's diameter, relative sliding speed and material attributes on the transient temperature field and stress field. The results demonstrates that the thermal stress caused by the wheel/rail friction is on the same scalar level with the stress caused by the mechanical load, the temperature rise and thermal stress are in direct ratio to the relative sliding speed, thermal expansion coefficient and Young's modulus, and are in inverse proportion to wheel's diameter and the specific heat.