Base on the investigation of lubrication property of gear oil GL 5, the variation of contact pressure carried in the contact zone was discussed.The worn tests about the lubricant GL 5 were performed under two temperatures of 20 ℃ and 100 ℃ using a four ball tester, the variation of wear scar diameter with load was analyzed, and the contact pressure characteristic was discussed.These results show that temperature plays the role on GL 5 lubrication, and the maximal non seizer load is decreased from 1 236 N to 981 N when the temperature is increased from 20 ℃ to 100 ℃.Contact pressure undergoes through initial increased then decreased change with the load.As the load exceeds the maximal non seizer load, contact pressure is decreased sharply, and the dimensionless characteristic parameter of the Streibeck curve is significantly increased.Coefficient of friction functions as non linear increase with load, and the temperature has little effect on the coefficient of friction.If the lubricant GL 5 bears higher contact pressure, its load capacity should be improved.