The viscosity of three kinds of lubricant oils for different periods and new oil were measured by Viscosity Tester.The tribological properties of four kinds of oil samples were investigated by UMT-II friction and wear tester.The tribological properties of three kinds of used lubricant oils after adding antiwear additive were also analyzed.The results show that the viscosity of used lubricant oils is decreased and then increased with the increase of running mileages.With the increase of running mileages,the friction coefficient of the lubricant oils is increased,and the wear rate of the test ball is also increased.The antiwear additives have different influence on the used lubricant oils in different periods,and they are beneficial to the antiwear performance of the lubricant oil at rapid wear stage.