Based on cold cathode electron emission mechanism, a gas discharge electron beam (EB) gun and its electron optics system had been designed. In order to meet long time work requirement, three-stage AC–DC topology circuit, the circuit of transformer primary side parallel connection and output rectifier circuit series connection to obtain high voltage, double closed-loop control and discharge protection had been adopted to manufacture a inverter power supply. The output beam current of gas discharge electron beam source, which adopted mentioned above technology, is up to –20kV/1500mA. The experimental results show that, when the inert gas is used as the discharge gas, the electron beam current of the gas discharge EB gun will decrease for a long time. When the air is used as the discharge gas, the output characteristic of low voltage and high current is shown. When airflow rate of He, Ar or air is less than 0.03L/min, the output electron beam current increases with acceleration voltage increased. When the constant acceleration voltage is given, the output beam current increases gradually with the He airflow rate increased. The voltage and current waveforms of IGBT bridges in the third stage AC–DC circuit are well accordance, which will meet the need of long time stable operation and high power output.