The reason of Caohai water pollution in Weining County, Guizhou Province is that the total amount of sewage discharge is increasing. According to the International Environmental Protection Network, with the social and economic development and the acceleration of urbanization in Weining County, the main sources of water pollution are domestic sewage of residents in Weining County, rainwater in the early stage of the county and agricultural pollution sources around Caohai, and the discharge of a large number of domestic sewage seriously pollutes the water quality of Caohai.