Abstract: Continuous culture has become an important method to study the competition between toxic and non-toxic Microcystis. Under the continuous culture mode, the growth of Microcystis is not limited by nutrients and harmful metabolites, and its growth rate and metabolic activity are relatively constant. At this time, the growth of Microcystis is only controlled by single or multiple factors set by experimental conditions, and less influenced by other non-experimental factors. A continuous algal culture system was constructed by adding an external ring light source to the chemostat, and the optimal culture conditions were obtained by optimizing feeding time, inoculation density and dilution rate parameters, which were applied in the competition experiment between toxic Microcystis PCC 7806 and non-toxic Microcystis PCC 7806 mcyB^–. The optimal culture conditions for continuous culture were the 4th day for the feeding, the initial seeding density at 4×10⁶ cells/mL and 0.15/d for the dilution rate. Under continuous culture, 1﹕1 ratio of toxic and non-toxic Microcystis inoculation were balanced at the beginning, with non-toxic Microcystis dominating later, and then remained unchanged for a long time with different degrees of dominance. On this basis, the influences of different light intensities on the competition between toxic and non-toxic Microcystis were carried out. The results showed that when the light intensities were 35 and 80 μmol/(m²·s), non-toxic strains dominated in continuous culture; while the light intensities were 5 and 15 μmol/(m²·s), the ratio of non-toxic and toxic Microcystis remained unchanged. The optimization of algal continuous culture system provides a suitable culture mode for indoor algal competition test. Besides, the influence of light intensity on toxic and non-toxic Microcystis provides technical support for exploring the competitive succession mechanism.