Abstract: Abstract: In order to explore the influence of three different light intensities on the community structure of symbiotic biofilm of bacterial-algal. We designed three test systems on different light intensity levels (CK group 0 lx, T1 group 4 750 lx, T2 group 7 580 lx) to study the community structure of bacteria in the symbiotic biofilm of bacteria and algae under the water quality condition of freshwater aquaculture pond. The results showed that the development of bacterial community structure had different response to different micro ecological environment. The number of OTUs (498.5±7.16, 517.2±10.36), Chao1 index (648.7±35.64, 672.8±30.69) and Shannon index (4.68±0.01, 4.85±0.03) were significantly higher than CK (406.6±8.18, 521.5±18.62, 3.53±0.02). In CK group, the number of bacterial community in biofilm was in a weak position, which was significantly lower than that in T1 and T2 treatments. With the increase of light intensity, the order of dominant bacterial groups in the biofilm changed. In CK group, Proteobacteria was dominant, Bacteroidetes, chloroflexa and actinobacteria were second, Acidobacteria and verrucomibia were in a weak position. In T1 group, Proteobacteria, Bacteroidetes and Chloroflexi were dominant, Actinobacteria, Planctomycetes and Cyanobacteria were second, Acidobacteria, Verrucomicrobia and Nitrospirae were in a weak position. In T2 group, Bacteroidetes, Chloroflexi and Cyanobacteria were dominant, Proteobacteria and Planctomycetes were second, Actinobacteria and Acidobacteria were in a weak position. In CK group, the mean value of phylum richness of Proteobacteria was 32.92%±2.65%, which was significantly higher than that in T1 group (21.89%±3.25%) and T2 group (15.28%±3.60%) (P < 0.05). The abundance of Bacteroidetes in T1 group was 18.72%±2.48%, and that in T2 group was 19.78%±4.69%. There was no significant difference between the two groups. The abundance of Bacteroidetes in CK group was 14.24%±1.89%, significantly lower than that in T1 and T2 groups (P < 0.05). The abundance of Chloroflexi in CK group was 13.34%±3.73%, significantly lower than that in T1 group (17.57%±3.57%) and T2 group (18.77%±3.14%) (P < 0.05). The abundance of Nitrospirae in CK group and T1 group was 2.61%±0.53% and 2.45%±0.34%, respectively, which was significantly higher than that in T2 group (0.94%±0.1%). There was no difference in the abundance of Actinobacteria between T1 and T2 groups, but there was significant difference between them and CK group. The abundance of Cyanobacteria in CK group (1.59%±0.52%) was significantly lower than that in T1 group (9.24%±1.2%) and T2 group (20.03%±1.03%). The relative abundance of Nitrospira in CK and T1 was 2.72%±0.93% and 2.57%±0.46%, significantly higher than that in T2. The relative abundance of Rhodobacter increased with the increase of light intensity. The mean relative abundance of Pseudomonas in T1 group was significantly higher than that in CK group and T2 group. The development of bacterial community structure in the biofilm of Bacillariophyta had different response to different light intensity.