Abstract: Azolla has high growth and propagation rate, strong photosynthetic O2-releasing ability and rich nutrient value. It is able to be used as salad-type vegetable, and can also be cultured on wet bed in multi-layer condition. Hence, it possesses a potential functioning as providing O2, fresh vegetable and absorbing CO2 for Controlled Ecological Life Support System in space. In this study, we try to make clear the O2-providing characteristics of Azolla in controlled close chamber under manned condition in order to lay a foundation for Azolla as a biological component in the next ground simulated experiment and space application. A controlled close test chamber and Azolla wet-culturing devices were built to measure the changes of atmospheric O2-CO2 concentration inside chamber under "Azolla-men" coexisting condition. The results shows that, at 7000－9000 Lx of artificial light intensity, Azolla were grown under wet-culturing condition, people respiration and Azolla photosynthesis complemented each other, the atmospheric O2-CO2 concentration inside chamber maintained equilibration. According to theoretical calculation, about 10 m2 Azolla can basically meet an astronaut’ needs of O2. Elevated atmospheric CO2 concentrations in close chamber have obvious effects on enhancing Azolla net photosynthesis efficiency. This shows that Azolla has strong photosynthetic O2-releasing ability, which equilibrates the O2-CO2 concentration inside chamber in favor of human survival, and then verifies the prospect of Azolla in space application.