The operating principles of automatic tracking voltage frequency and phase angle selection in the electrical apparatus measuring device that are urgently needed are described. The methods of calculating frequency and phase are based on Fast Fourier Transform Algorithm(FFT). A microprocessor using FFT algorithm generates the phase controlled signal according to sampling instantaneous value of voltage. The hardware mainly includes the structure based on STM32F103, the signal amplifying circuit, the insulation blocking and power switch circuit, and the touch screen circuit. The error sources of measuring and data processing are analyzed, and the methods that how to improve the measurement accuracy are discussed in this paper. The system of electrical apparatus measuring device for phase angle selection is reliability and the precision is ±1°. The practice shows that this method of automatic tracking voltage frequency is of certain value for reference to rapid calculation of phase angle selection.