The paper is aim to analyze the changing of river water quality of Beijing during 2009 to 2017，and to provide the legislation basis for protecting Beijing water resources. The research results shows that，Chaobai river had the best average water quality of the Beijing’s five river systems；the average water quality of Daqing river and Jiyun river systems demonstrated a trend of steady improvement；the average water quality of Beiyun river and Yongding river systems，however，were not significantly improved that remained at the level of inferior V water quality. The suggestion is：we should improve the Beijing Water Environment Report，establish independent assessment agency for the institution of River Chief，explore the collaboration between polluting enterprises and social capital to finally solve the problems of water pollution in Beijing.