Based on the water ecology survey results of 24 major drinking water sources in Fujian Province in the summer of 2021, the characteristics of phytoplankton community structure and nutrient status of reservoirs were analyzed. The phytoplanktonic index of biotic integrity (P-IBI) was constructed using three biological parameters, total phytoplankton density, Shannon-Wiene diversity index, and proportion of cyanobacteria density to evaluate the health status of the Shaxikou Reservoir and the Dongzhang Reservoir. The results show that the phytoplankton community structure of most reservoirs in Fujian in 2021 was dominated by Cyanophyta-Chlorophyta-Bacillariophyta, and 60.9% of the reservoirs were dominated by Cyanobacteria. The comprehensive nutrient status index ranged from 24.3 to 51.7, with an average value of 40.3. The eutrophication degree of reservoirs was low, but some reservoirs still had the risk of eutrophication. The P-IBI score of the Shaxikou Reservoir was 79.7, which was in a healthy state, while the P-IBI score of the Dongzhang Reservoir was 59.0, which was in a sub-healthy state. The evaluation results of P-IBI are in good agreement with the results of the multi-index evaluation method in the Blue Book of River and Lake Health Assessment of Fujian Province in 2021 . The evaluation method based on phytoplankton integrity index is effective and applicable.