The various disturbances destroy CNC system tracking accuracy greatly. The ideal servo system should obtain high system precision and machining precision even if under disturbances action. The influence of electric disturbances to CNC servo system is researched in detail. Moreover, the electric disturbances on the electric interface of servo system driver elements are observed, and the observe compensation quantity is added to the position controller output. The simulations aimed at saw-tooth wave electric disturbance signal show that the developed approach can reduce tracking error and enhance the restrain disturbance characteristic.