The invention discloses an indoor microalga culture system. The indoor microalga culture system comprises an opening type culture device, a carbon dioxide supplying device and a light illumination device, wherein the light illumination device comprises a mounting base, a lamp tube and a light source; the mounting base is mounted on the opening type culture device; one end of the lamp tube is mounted on the mounting base, and the other end of the lamp tube stretches into the opening type culture device; the lamp tube is fully filled with heat-transferring liquid. The invention further discloses an indoor microalga culture method; the indoor microalga culture method comprises the following steps: pouring seawater and nutrient salt into the opening type culture device as a culture water body; introducing CO2 gas into the culture water body; after the concentration of microalgae reaches 3.0*10<6>cfu/mL, collecting 55 percent to 75 percent of algae in the culture device; after collecting the algae, supplementing the seawater and the nutrient salt; after 42 days, extracting all the algae; flushing the culture device with an EDTA (Ethylene Diamine Tetraacetic Acid) solution; then flushing the culture device with high-salinity bittern; finally, flushing the culture device with fresh water. According to the indoor microalga culture system and method, disclosed by the invention, the light illumination obtaining quantity in a unit area of the algae is increased; the production efficiency of the microalgae is improved, and energy sources are saved.