The symbiotic cyanobacteria were isolated from the sporangium of Huperzia. Serrata (Thunb.) Trevis (H. Serrata). And the effects of light intensity on the growth of cyanobacteria were studied. The results showed that the optimal biomass of cyanobacteria cell was obtained under 500 Lx light intensity. The higher light intensity (> 2000 Lx) repressed the cyanobacteria cell growth which would be faded and turned white. During the growth of symbiotic cyanobacteria, the chlorophyll a content was significantly reduced with the light intensity increased, which were positively correlated with the biomass reduction under higher light intensity. In addition, we found that the biomass and the chlorophyll a content of symbiotic cyanobacteria were higher under green light or blue light than those under red light. In conclusion, the weak light was suitable for the growth of symbiotic cyanobacteria isolated from the sporangium of H. Serrata. And the optimal light quality on the growth of symbiotic cyanobacteria was green light or blue light.