Fretting wear behavior of 40CrNiMoA steel was studied on a SRVⅣoscillating friction and wear tester. The results indicate that the fretting wear volume increase with test frequency, load and amplitude increasing. Meanwhile, the fretting wear mechanism is directly related to test frequency, load and amplitude. When they are small, the main fretting wear mechanism is abrasive wear, with these test parameters increasing, the main fretting wear mechanism turns to a combination of abrasive wear and adhesion wear. Based on the experimental results, the anti-fretting wear measures of steel worm gear pairs used in mechanical tracked regulator of tracked vehicle are discussed.