In 2017, a large reservoir named Qingcaosha in Shanghai built an ecological slope protection. In order to explore its impact on the structure of the phytoplankton community, a monthly survey and comparison study of the phytoplankton community in the ecological slope protection area of the reservoir and the control area in the reservoir was carried out in 2018. A total of 201 species of phytoplankton in the ecological slope protection area and 194 species in the control area in the reservoir were identified. The species in the two regions were moderately similar, and the species composition was both Chlorophyta-Bacillariophyta-Cyanophytatype. The dominant species in the ecological slope protection area and the control area of the reservoir mainly belonged to Chlorophyta and Bacillariophyta, which were basically the same. The dominant species with a high degree of dominance were Aphanocapsa sp., Pseudanabaena limnetica, and Cyclotella sp. and Aulacoseira ambigua. The annual mean biological density and biomass of the community atecological slope protection areawere (578.46±455.30)×10⁴ cells/L and (1.55±1.03) mg/L, respectively, and those of the control area in the reservoir were respectively (663.46±588.67)×10⁴ cells/L and (1.61±0.98) mg/L. There was no significant difference in phytoplankton stock between the two areas (P>0.05). The PCOA analysis of the principal coordinates showed that there was no significant difference in phytoplankton community structure between the ecological slope protection area and the control area in the reservoir (P>0.05). The above results all demonstrate that the construction of the ecological slope protection has little impact on the phytoplankton community of the reservoir.