The overall performance of excavator is contingent upon the performance of hydraulic excavator travel motor. Relief valve of the travel motor plays an important part in life of the travel motor. High temperature low overflow pressure will cause inability to walk. The study on the relief valve overflow pressure under high temperature was focused on. Based on the mathematical model of the relief valve, the decisive factors were researched. According the spool with different gap, the analysis of dynamic simulation was made. On the basis of the simulation results, the associated experiments were conducted. The experimental results show that the gap plays the decisive part in relief pressure.