Abstract: The zero current switching quasi resonant converter for high power Fast Axial Flow CO2 gas laser is studied in this paper.The operating principle and circuit structure of the power supply are discussed.The resonant converter is simulated by computer and the operating waveforms are obtained.Compared with the PWM hard switching converter,the outstanding characteristics of the ZCS-QR converter are presented.The resonant converter is especially attraction for high frequency,high power application.