Abstract: The air control system in a manned spacecraft is used to control theoxygen partial pressure and the air pressure of the pressurized cabin within the index range. In the manned spacecraft for a long-term crew staying, the water electrolysis system is usually used to control the oxygen partial pressure of the pressurized cabin. A simulation model of the air pressure control system of the pressurized cabin in the manned spacecraft is proposed. Using this model, the varying trends of the oxygen partial pressure and the air pressure related to the two oxygen supply modes of the water electrolysis system and the oxygen cylinder are compared and analyzed. According to the results, when the staying period is 24 h, the oxygen partial pressure related to the oxygen supply by the oxygen cylinder keeps declining, which is different from that related to the oxygen supply by the water electrolysis system. The varying trend of the oxygen partial pressure related to the oxygen supply by the water electrolysis system is determined by the oxygen supply flux and the crew metabolic oxygen consumption; meanwhile, the varying range of the oxygen partial pressure related to the oxygen supply by the water electrolysis system is dramatically smaller than that related to the oxygen supply by the oxygen cylinder. When the staying period is 60 d, the varying cycle of the oxygen partial pressure and the air pressure related to the oxygen supply by the water electrolysis system is dramatically longer than that related to the oxygen supply by the oxygen cylinder. In order to avoid the influence of the air temperature, the control range of the oxygen partial pressure and the air pressure should be narrower than the allowable range.