A bioregenerative system model based on photosynthesis of unicellular algae has been created and studied. It includes man and microorganisms. The regeneration of substances vital for man in the model achieves 90%. Besides regeneration of atmosphere, water and partly food, a series of secondary functions is performed by the system. All functional characteristics were stabilized either at once or after some transitory period, and were close to the control. The environment formed in the system met biological needs of man.The system model is a transitory stage on the way of creating systems, more complex in structure and closure degree. It has a practical significance as a bioregenerative system and may be used in present-day astronautics practice.