A method for phase calculating by spoilal averaging over shift ESPI optical field is proposed based on the principle of phals-shifting interferometry. It is possible to realize phase shifter calibration automatically with the same optical system, and to obtain the measurement characteristics of the optical field and the Phase shifter. We have compared this method with equidistant fringe phase calibration, and the relative error between the two ways is less than 3%, within the usable voltage range.