To illustrate pollution characteristics of atmospheric dry and wet phosphorus deposition of reservoir in the typical sand source area and their contribution to the water phosphorus pollution in order to provide scientific basis for governance of the reservoir eutrophication, we set 12 atmospheric precipitation monitoring sites along the reservoir shore in 2014 in Dahekou Reservoir area in sand source areas of Beijing-Inner Mongolia, and collected dry and wet sedimentation samples to determine concentration of total phosphorus (TP) in dry and wet subsidence and to calculate the yearly and monthly fluxes and the annual storage of TP loading. The results showed that atmospheric TP dry and wet deposition had significantly seasonal differences in the study area. The TP dry deposition flux ranged between 4.89-35.76 kg/(km²·month)in the year, and was mainly concentrated in the spring (April) and autumn (October). The maximum of TP dry deposition flux appeared in the most serious sandstorm month of spring (April). Wet deposition was mainly concentrated in the summer (June to August). The maximum of TP wet subsidence flux appeared in the largest rainfall month (August), and its value was 28.88 kg/(km²·month). The TP wet subsidence flux was significantly positively related with rainfall. Atmospheric pollutant load of TP subsidence storage was 0.719 t in 2014, and the ratio of TP pollution load of both Luan River and Tuligen River storage was 51.17% in the same period. They have become one of the important source term of influencing and restricting the phosphorus nutrient levels in Dahekou Reservoir.