The effects of friction speed and ultrasonic vibration on friction reduction and anti-wear properties of GCr15/45# steel frictional pairs under oil lubrication were investigated by a modified MFT-R4000 reciprocating friction and wear tester. The mechanism of friction reduction and anti-wear under ultrasonic vibration was discussed. The results showed that, the ultrasonic vibration could influence the friction reduction and anti-wear properties of frictional pairs due to it could reduce the stress between the friction pairs and destroy the oil film on the surface of samples. When the friction frequency was 2Hz，ultrasonic vibration would reduce the friction coefficient and wear volume of the frictional pairs. When the load was 40N, the friction coefficient and wear volume of the frictional pairs attained under ultrasonic vibration decreased 8% and 44% respectively. However, ultrasonic vibration would increase the friction coefficient and wear volume when the friction frequency was 5Hz. When the load was 30N, friction coefficient and wear volume of frictional pairs increased 11% and 74% than that without ultrasonic vibration respectively.