In order to reduce the number of invalid operators of PI hysteresis model, and to improve the operation speed of the model, the threshold optimization method is adopted to improve the PI model. When PI hysteresis model is used to fit the measured curves of an object, the slope of the measured curve can be expressed by the weight sum of the operator at each threshold point, the smaller difference between the weight sum and the curve slope, the higher accuracy of the PI hysteresis model. In this way, the threshold of PI hysteresis model can be optimized, and the operator number can be reduced, when the model accuracy meets the requirements and the accuracy is same at each threshold. According to the maximum measured lifting curve, the hysteresis model of a piezoelectric micropositioning stage is established based on the threshold optimization method. The experimental results show that the numbers of the model operators are only 7, and they do not contain the invalid operators; within the displacement range of 0~15.94 μm, the error range of the model is 0.23~0.40 μm, that is 1.4%~2.5%. The model can better describe the hysteresis nonlinearity of the piezoelectric micropositioning stage.