In order to explore the tribological law of the ball joint pair coated with ZrO2 in the hydraulic motor,the friction and wear changes of the ball joint pair coated with ZrO2 in the hydraulic motor under different loads and speeds were simulated by using a friction and wear tester and a white light interferometer.The friction and wear law was analyzed from the friction coefficient,wear volume and wear trace morphology,and the optimal working condition was found to improve the service life and working efficiency of the ball joint with ZrO2 coating.Through the control variable test,it is found that the influence of rotating speed on the tribological properties of ZrO2 coated ball joint is much greater than the load,and the minimum friction coefficient is 0.059 6 at 100 N-100 r/min; the wear volume increases gradually with the increase of load and speed,and the minimum wear volume is 0.184 mm3 at 50 N-50 r/min.Based on the above laws,it is found that the friction reduction and anti-wear effect of ZrO2 coated ball joint pair is the best under the working conditions of load 100 N and rotating speed 50 r/min.Low rotating speed can effectively prolong the service life of hydraulic motor and improve mechanical efficiency.