Abstract: HL-2A device makes use of a pulse generator set to provide energy to the thyristor power supply, which is phase-controlled, thus the quality of the synchronization signal will directly affect the control accuracy of the power supply. The synchronization signal of the thyristor power supply in HL-2A device is taken from the synchronous transformer. The power supply mode of the pulse generator unit with rectifier load makes the synchronization signal not only have serious distortion, but also have the characteristics of a wide frequency range. Considering the characteristics of the synchronization signal, point-by-point Butterworth filter is implemented to eliminate waveform distortion, and then high quality synchronization signal is obtained by real-time calculation of frequency and phase reconstruction. Based on NI CompactRIO device, a real-time processing system for synchronization signal of thyristor phase-controlled power supply is designed. The experimental results show that the system can effectively solve the problem of serious distortion and wide-range frequency change of synchronization signal.