Water environment deterioration is critic to the health of lake ecosystem,and trend analysis is considered as the very first step to mitigate water pollution.Based on pollutants monitoring data from 1980 to 2011 in Lake Fuxian,trends of COD_Mn,TN, TP,SD,Chl.a and phytoplankton abundance are quantified using Mann-Kendall and Daniel trend test methods.From the perspectives of human impacts and natural changes,9 indices of driving forces are selected to build the grey relationships between driving factors and water quality.Results show that (1) six indices of water quality changed greatly during the period of 1980-2011, among which TP,TN and phytoplankton abundance fluctuated the most with coefficient of variations greater than 0.6;(2) COD_Mn, TN,SD,Chl.a and phytoplankton abundance showed significant degradation at 0.05 significance level,and results of Mann-Kendall and Daniel are consistent;(3) significant correlation was found between water quality index and selected driving factors in which human population and water temperature are identified as the main factors with correlation coefficient values higher than 0.7.