By taking the two kinds of high-speed vehicles of yaw damper of our country as examples, the oil temperature effect on dynamic feature of yaw damper and vehicle stability is mainly analyzed. Dynamic feature of yaw damper under different temperature was investigated based on experiment. The study indicates that yaw damper absorbs more energy, and dynamic stiffness and dynamic damping also increase with the decreasing of oil temperature when oil temperature is within normal working limits, otherwise they would be decreased. Then a SIMPACK model of highspeed vehicle was built to study oil temperature effect on vehicle stability. It is concluded that vehicle stability has no obvious difference within 200 km/h. While speed is bigger than 200 km/h, vehicle stability becomes worse. On the whole, oil temperature has less influence on vehicle stability.