In order to understand the pollution characteristics of Dianchi watershed and to propose targeted countermeasures, the study investigated the variation of pollutant load into Lake Dianchi as well as the composition and spatial distribution characteristics. The result showed that the generated and reduced amounts of point source pollutant increased continually during 1988 and 2014, and the discharged amount was decreased. The pollutant load of urban non-point source grew as a result of the expansion of built-up areas. The pollutant load of agricultural non-point source peaked in the 1990s and then decreased. In the Dianchi watershed, COD was mainly from urban non-point source, total nitrogen was mainly from effluent of wastewater treatment plants, and total phosphorus was mainly from agriculture non-point source and point source but without the pollutant collection. Urban non-point source and non-collected point source had become the main sources of pollutants for most watershed sections. To solve the pollution problems of the Dianchi watershed, the local government should persist in point-source control, pay high attention to urban non-point source control and make good effort in agriculture non-point source control, so as to build a sound pollutant collection and treatment system.