Excessive backlash seriously influences machining precision of CNC lathe. The cause of poor machining precision was excessive backlash of X axis through analyzing the machining route.Aiming at excessive backlash and too much load of the motor, troubleshooting was made. It was found that mechanical deformation of turret’〖KG-*2〗s table and ball screw was the real causes of excessive backlash and too much load. The real cause of poor machining precision was analyzed, maintenance process and ways were illustrated, and suggestions about maintenance and machine were presented.