In the view that the current testing method for the electric parameters of ultrasonic motor cannot characterize the variation of its transient electric parameters in starting up state， a method for testing the electrical parameters of ultrasonic motors in starting transient state is proposed. In this paper， the drive voltage and current signals of the ultrasonic motor are analyzed by windowed short-time Fourier transform， then the frequency spectrum of the voltage and current signals is obtained. Based on single peak spectral lines interpolation algorithm， the accurate amplitude， frequency and phase of the signals could be obtained from the frequency spectrum. By processing and analyzing the simulation signal， the accuracy of the method in the instantaneous electric parameter calculation is verified. A PMR-60/E ultrasonic motor is tested using the ultrasonic motor transient testing platform. The results show that this method can reveal the variation of the transient electrical parameters of ultrasonic motor in the process of motor starting， and can be used to evaluate the vibration response characteristics of ultrasonic motor. It can provide important information for the establishment of the equivalent circuit model of ultrasonic motor and the design of the driving circuit at the same time.