Abstract: In this study, we try to investigate the O₂-supply characteristics under manned condition in order to lay a foundation for carrying out Azolla biological component systematical and general ground simulation experiment and space application. A closed test cabin of Controlled Ecological Life Support System and Azolla wet-culturing devices were built to measure the changes of atmospheric O₂-CO₂ concentration inside the cabin under “Azolla-fish-men” coexisting condition. The results showed that, O₂ consumption amount per unit weight of fish is 0.0805～0.0831L·kg^-1·h^-1, the CO₂ emission amount is 0.0705～0.0736L·kg^-1·h^-1. Which of trial volunteers is O₂ 19.71L·h^-1 and CO₂ 18.90L·h^-1 under 7000～8000 lx. Artificial light, human and fish respiring and Azolla photosynthetic O₂-releasing tend to achieve O₂-CO₂ homeostasis inside the cabin. Enhancing atmospheric CO₂ concentrations in the cabin obviously promoted Azolla group net photosynthesis efficiency. This shows that Azolla has strong photosynthetic O₂-release ability, which equilibrates the O₂-CO₂ concentration inside the cabin in favor of human survival, and then verifies the prospect of Azolla in space application.