Aimed at the water quality condition of Poyang Lake and based on the monitoring data of 14 representative monitoring stations,the current situation of water quality change is analyzed and the trend of water quality change is forecasted by the fuzzy mathematics method.The results showed that the fuzzy mathematics method can more objectively reflect the situation of water environment quality,also found that the water quality of Poyang Lake,into Poyang Lake and outlet of Poyang Lake is overall good and have the improved trend.After the pollutants into the southern lake was diluted and degraded,the water quality in the downstream is better than upstream.The main pollutants in this lake are ammonia nitrogen and total phosphorus.The site of serious pollution is the outlet of Lean River.