In order to understand the stability of the phytoplankton species diversity structure of the Huaxi Reservoir on the Guizhou Plateau after the ecological regulation of cyanobacteria blooms in March of 2017, the phytoplankton community structure of Huaxi Reservoir was investigated in the four seasons from April 2017 to January 2018. The relationship between the main phytoplankton communities was comprehensively analyzed using niche width, niche overlap, variance ratio method, Chi-square test, and connection coefficient. The results showed that there are 4 Phylum and 11 Genus in four seasons, among which Synedra acusva and Cylotella meneghiniana were the dominant species in 4 seasons, which indicate the state of the water environment. The niche width of each dominant species is quite different, the variation range is 0.120-0.814, mainly composed of wide niche species and narrow niche species. Niche overlap between species pairs varies from 0.101 to 0.936, the more similar the habitat, the greater the overlap value. Variance ratio method analysis shown that the dominant species pairs are generally positively correlated. The Chi-square test shows that 9 pairs of 38 pairs of algae species are significantly connected, mainly distributed in summer and autumn, reflecting the great influence of human disturbance and seasonal changes on the community structure of Huaxi Reservoir, showing a cross succession model of “unstable-stable-unstable”.