The tribological characteristics of highspeed rail gear oils were explored through fourball machine tribological test method.The friction experiments were carried out for two kinds of gear oils under the temperature of 75 ℃ and test time of 1 h by adopting the combination of speed and load conditions.Test results show that the change of load and speed has influence on the friction coefficient of two kinds of gear oils.At constant speed and variable load,the grinding spot of the steel ball shows a trend of gradual increase in the size with the increasing of load,and at constant load and variable speed,the grinding size shows a trend of decrease after the first increase with the increasing of speed.The load has a more obvious influence on grinding spot size.By comparing the test results of two kinds of oils,it can be found that the oil with good abrasion resistance also has stable friction coefficient,and the maximum grinding spot is obtain for two kinds of oils under the conditions of 1 400 r/min and 353 N.