Abstract: Taking a middle-sized reservoir as the research target, Arc-GIS technology was applied to analyze the catchment and the surrounding land use in order to study the cause and control technologies of reservoir. The main source of total phosphorus (TP) pollution and the key pollution area were analyzed and the pollution control technologies were proposed based on the study. The results showed that the inflow river one, accounting for 91.8% of the total runoff, is the main runoff source of reservoir. The pollution load of agricultural non-point source is estimated to be about 807.84kg/a and the contribution rate is 72.53% of the total pollution load. Therefore, agricultural non-point source is the main source of TP pollution in reservoir, followed by pollution from livestock and poultry. Different water quality objectives have different reservoir capacity and pollution reduction rate. Under the conditions of class III and class IV water quality objectives, the capacity of receiving total phosphorus (TP) pollutant is 363.73kg/a and 727.45kg/a respectively and the pollution reduction rate is 67.34% and 34.69% respectively. Considering both the objective accessibility and the lower cost of engineering, the wetland treatment and composite ecological floating land are the optimal technologies to control non-point pollution and achieve the objectives.