The traditional PI hysteresis model is improved as to build both high accuracy and fast computing speed of hysteresis model of the piezoelectric micro positioning stage.Based on the fact that the slopes of the first half of the initial loading curve for the piezoelectric micro positioning stage change much while the slopes of the second half change little,the PI hysteresis model of the stage was established by the non equinterval threshold value. The established model was identified by optimizing the minimum norm of the errors between measured initial load curve and the model.The experimental results show that the maximum error and average error of the model are 0.71 μm and 0.23 μm in the displacement range of 20.7 μm.