By investigating water quality of Gehu Lake from Apr. 2004 to Apr. 2005, an analysis is made to development trends of parameters such as diaphaneity, pH, DO, BOD, CODMn, TIN and TP. Eutrophication evaluation was carried out by calculating eutrophication status index of Gehu Lake and contrasting with eutrophication status in twenty years. The results arrived as DO in summer is 3.98 mg/L, BOD average is 4.98 mg/L over the year, CODM, average is 4.59 nag/L, TIN average is 1.37 mg/L and TP average is 0.209 mg/L. Getting rid of the later-mesotrophy stage in south, the eutrophication status of Gehu Lake is eutrophy stage. And the grade weakens gradually from north to south. It is the primary reason of eutrophication that the content of phosphorus and nitrogen in the water body has risen evidently. Water quality of upriver deteriorates and the dense aquatic culture causes pollution, and environmental functions have been damaged and nutrition has accumulated.