Long-term tracking, positioning and evaluating lake eutrophication are key for water areas to achieve their due functions. Given the feasibility, monotony and subjectivity of weight assignment of index selection assignment in the evaluation method and fuzziness, randomness, dynamic and biological indicative of water quality change, this study combines extensive and comprehensive evaluation with investigation and indoor plankton measurements to construct comprehensive analysis method of combined extension. First, annual data from five representative observation stations in the Poyang Lake Basin were collected for five times (regularly once in two years during 10 consecutive years). The data were evaluated by the combined extension method, whereby the water quality eutrophication of the five sites is evaluated through the plankton indicator method. The maximum consistence of combined level obtained by two methods, i.e. biological indicator evaluation method and extension comprehensive analysis method, can be used as assessing grade for the combined method adopted in the study. The results show that:(1)Water eutrophication has been kept in a stable way and taken on positive changes in Poyang Lake since 2006. In 2010, the water of four observation sites reached the extent of eutrophication. However, in 2014,Toad stone and Poyang sites' water was improved to light-extented eutrophication; the water of Duchang, Kangshan, Xingzi reached the medium nutrition with improved water quality; (2)In terms of geographic location, the degree of eutrophication of the southern and western areas is better than that in the northern, eastern and central lake regions on the whole, indicating the heterogeneity of eutrophication across regions.