An alga microbe photosynthetic reaction system is used to circularly cultivate alga microbes and a culture medium infused in the system. The system comprises a photosynthetic reaction unit, a communicating unit, a pressure liquid infusion unit, an injection and oxygen discharging device, and a regulation area. The photosynthetic reaction unit is a light permeable pipeline. The injection and oxygen discharging device is assembled with an oxygen discharge can and a liquid collection can. By the connection and the functioning of the photosynthetic reaction unit, the communicating unit, the pressure liquid infusion unit, the injection and oxygen discharging device, and the regulation area, the alga microbe culture solution can circularly cultivate good quality algae in the system. The system further comprises a heating unit, a watering unit, and a light complement unit to control the ambient temperature and the light source to suit all kinds of algae.