In view of the serious sewer overflow pollution of the combined pipe network system and the black and odorous phenomenon of the receiving water body, taking the Yinchuan No.1 Sewage Treatment Plant area as an example, the SWMM model is adopted for the simulation study under the conditions of short duration design rainfall and typical year long duration rainfall. The response of the overflow discharge and overflow pollutant load of the study area to different rainfall conditions and their impact on the water quality of the receiving water body are simulated and analyzed. The results show that in rainy days, the overflow and overflow pollution load of the combined pipe network system were large, and they increased with the increase of rainfall under both short-term and long-term rainfall conditions. The overflow pollution in front of the plant was highly concentrated, which exceeded the self-purification capacity of the receiving water body, and the water quality was in a black and odorous state in a short time. This study is of important referential value to the treatment of black and odorous water and the formulation of overflow pollution control plan in Yinchuan City.