The invention relates to a method for preparing and collecting oxygen-enriched air, belonging to the technical field of environment protection. The method mainly comprises the following steps: absorbing CO2 by microalgae, monitoring the pH value on line, producing oxygen by microalgae photosynthesis, monitoring dissolved oxygen concentration on line, collecting the oxygen-enriched air, determining oxygen content and comprehensively applying the product. In the invention, the microalgae is unicellular organism, has rapid growth speed, and has a rapid process in which the CO2 is absorbed and the oxygen is produced; a sealing system is used in the invention, the concentration of the oxygen in the oxygen-enriched air is relatively higher, so the collection is easier. As oxygen is wasted if being directly discharged into air, the invention can save energy and improve benefits effectively by collecting and using the oxygen.