Xichong River in Sichuan Province,a tributary of Jialing River,has been polluted seriously.In 2009,water quality of Xichong River was assessed to be the bad fifth grade through monitoring and analysis.The main contaminants in the river are ammonia nitrogen,chemical oxygen demand,total nitrogen,total phosphorus,and fecal coliform.By taking the Nanchong segment of Xichong River as the research object,the data from water quality monitoring at Leidashi and Laladu observation sites from 2003 to 2009 are analyzed based on blind number theory.As for the water environment capacity at the two sites,CODCr is found to be 637.01 kg/d and NH₃—N,0.76 kg/d.Chemical oxygen demand(W_CODCr) and ammonia nitrogen(W_NH3—N) exceeding the standards at the two sites are 874.59 and 116.34 kg/d,being 1.37 times and 153 times of the allowed value,respectively.In order to reach the third grade of national water quality standards,it is urgent to control the pollution of Xichong River.