Abstract: It is necessary for electronic transformer to make calibration before putting it into practice. A new calibration method is presented in order to solve existent problems of actual calibration course. The frequency of power system is accurately measured according to the combined measurement principle of the limited iteration and the least squares method. The quasi-synchronous algorithm is introduced, some key parameters and steps are especially discussed, and thus the accuracy of the calibration method influenced by the frequency vibration will be significantly improved. The simulation results of new calibration method is achieved, and it is well coincide with the testing results. It shows that the performance and efficiency of new calibration method is satisfied. It will provide the powerful theory support for the development of portable intelligent calibration equipment.