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Control model of ultrasonic motor is the foundation for high control performance .The frequency of driv-ing voltage is commonly used as control variable in the speed control system of ultrasonic motor .Speed control model with the input frequency can significantly improve speed control performance .Step response of rotating speed is tested .Then ,the transfer function model is identified through characteristic point method .Considering time-varying characteristics of the model parameters ,the variables are fitted with frequency and speed as the inde-pendent variables ,and the variable model of ultrasonic motor system is obtained ,with consideration of the nonlin-earity of ultrasonic motor system .The proposed model can be used in the design and analysis of the speed control system in ultrasonic motor .