Abstract: The oxygen concentration control in the extra-vehicular activity is important for the safety of astronauts and the success of the extra-vehicular mission. This paper analyzes the influencing factors of the oxygen concentration, and the proposes verification test methods on the oxygen concentration limits at a low pressure. A model is built to simulate the variation of the oxygen concentration, and the partial pressure of the oxygen and the module pressure control scheme during the extra-vehicular activity are designed.