Abstract: The operation of the Three Gorges Project has significantly changed the relationship between the river-connected lakes and the Yangtze River, thus affecting the water environment of the river-connected lakes. It was particularly important to effectively evaluate the water quality of Dongting Lake, the largest river-connected Lake in the Yangtze River basin. In 2019, monthly monitoring data were collected at 15 sampling sites in Dongting Lake, including nine water quality factors. The single factor index method, principal components analysis (PCA) method, Nemero pollution index method and Shannon-Weaver biodiversity index method were used to evaluate the water quality of Dongting Lake. The single factor index method could quickly and accurately evaluate water quality categories, and the Nemerow pollution index method was simple to calculate and widely used in water quality evaluation. However, the two methods could not accurately give the difference of pollution degree between different sampling points, and the Shannon-Weaver diversity index evaluation results were not consistent with the actual situation of some sampling points. To comprehensively consider the applicability and accuracy of different evaluation methods, it was recommended to use the PCA method to carry out Dongting Lake water quality evaluation. PCA method could not only reflect the main pollution index and its contribution rate, but also rank the pollution degree of different regional water bodies, and the evaluation results were objective and practical, so it was more suitable for the water quality evaluation of Dongting Lake region. However, in the daily work of water quality evaluation management, it was suggested that the single factor index method should be combined to determine the water quality categories, so as to ensure the effectiveness of management.