In order to improve the tribological properties of conventional gear oils,the gear oil with nanoNi powders was prepared by combining the dispersion methods of high speed shear and surface modifacation of nanoNi powders.The effects of high shear speed and time,KH560 dispersant addition and nanoNi powders addition on tribological properties of gear oils were studied by using fourball tester.The wear scar morphology and composition were characterized by means of SEM and EDS,and the antiwear mechanism was preliminary explored.The results indicate that the best dispersion effect of nanoNi powders in the gear oil is realized at the high shear speed of 3 000 r/min,shearing time of 30 min,and the KH560 weight of 6%.The gear oil with nanoNi powder weight of 0.5% has the best tribological properties,its friction coefficient and wear scar diameter are reduced by 25.5% and 22.6% respectively as compared to the gear oil without nanoNi powder.The gear oil with nanoNi powders has good friction reducing property at different loads,but only has good antiwear property at low loads.The results of wear scar morphology and EDS analysis show that the nickel powder added to the gear oil plays a part in filling furrows and repairing worn surface during the friction process.