This paper introduces the criterion of piezo actuators using strain gage for closed loop control. The method is based on the principle of electrical resistance, four strain gages are directly bonded on the surface of ceramic stack to form a Wheatstone bridge. With the displacement of ceramic stack, the bridge resistance will be changed and this change can be converted to the shift of voltage. The experiment data are studied to find the hysteresis behavior of piezo in different condition, and find that those hysteresis curves are similar in shape. Just based on this characteristic, one of the curves is employed to establish the model of control. The results with the feedback of strain gage show that the hysteresis of the piezo actuators can be eliminated and the repeatability can be as good as several nanometers.