Abstract: The Pudu River developed with the Pudu Fault and the Xiaojiang River with Xiaojiang Fault flowed into the Kunming Basin, then formed the Dianchi Lake on 3.40 MaB P. The Jinsha River linked in the late of Pleistocene, so the Pudu River and the Xiaojiang River flowed backwards to the Jinsha River, then the Dianchi Lake became the wind gap of the three water systems of the Jinsha river, the Zhujiang River and the Honghe River, and formed the hydrographic feature of the Dianchi Lake, such as a small replenishment coefficient and a long exchange water cycle. Because a great deal of pollutants were inputted into the Dianchi Lake and accumulated, the water quality in the lake declined rapidly. In order to treat the water environment in the Dianchi Lake, we suggest that the water in the Zhangjiu River should be diverted into the Tanglangchuan River at Luquan county, then the Zhangjiu River and the Tanglangchuan River would flow into the Dianchi Lake, so the area of gathering water for the Dianchi Lake will add up to 16 066 km2, and the annual surface runoff will add up to 26.64×108 m3, the exchange water cycle will reduce to 197.2 d. While we also advise to change the outlet of the Dianchi Lake by digging up a new canal at Kunming, and the pollutant will not diffuse all into the Dianchi Lake. The pollution in the Dianchi Lake will be controlled.

Key words: water environment, circulating water, exchange water cycle, the Dianchi Lake