Abstract: In order to meet the requirements of the surface potential control test for a cargo spacecraft, a gas supply unit used for the active control of the surface potential of the spacecraft is developed. The assembly is characterized by lightweight, small volume and compact structure, with the functions of the argon storage and the micro flow output. According to the leakage rate data obtained by the test and the flow-pressure characteristics of the flow controller, a mathematical model of the gas supply unit is established to describe the argon flow rate and the pressure of the gas cylinder against time. The effective on-orbit working time is calculated based on the model. It is shown that the on-orbit storage capacity and the micro-flow output capability of the gas supply component can meet the task requirements.