With　the　increasing　urbanization　rate,　higher　demand　is　placed　on　drainage　systems,　necessitating　analysis　of　their　risk　profiles.　While　many　studies　focus　on　the　individual　hydraulic　modeling　of　stormwater　and　wastewater　systems　when　considering　operational　risks,　they　often　overlook　the　exacerbating　effects　of　combined　stormwater　and　wastewater　flows　on　each　other＇s　risks.　In　this　study,　we　constructed　a　model　of　the　combined　stormwater　and　wastewater　drainage　system　in　Lijiao,　Guangdong　Province.　We　analyzed　the　operational　risks　of　both　stormwater　and　sewage　networks　in　different　scenarios,　focusing　on　full-load　pipes,　overload　pipes,　node　overflows,　and　minimum　flow　velocities.　Furthermore,　we　compared　the　exacerbating　effects　of　sewage　and　stormwater　on　each　other＇s　network　operational　risks.　Simulation　results　indicated　that,　for　sewage　networks　with　combined　sewer　sections,　the　lengths　of　full-load　pipes　and　overload　pipes　increased　by　an　average　of　27.4%　and　16.3%,　respectively,　during　rainy　weather　scenarios　compared　to　dry　weather.　After　considering　the　inflow　of　sewage　into　combined　sewer　sections,　the　average　length　of　full-load　pipes　increased　by　3.8　km,　overload　pipe　length　increased　by　1.1　km,　and　overflow　volume　increased　by　2.26　x　104　m3.　As　the　return　period　of　rainfall　events　increases,　these　inter-system　impacts　gradually　diminish.　Therefore,　when　modeling　drainage　systems　and　assessing　operational　risks,　particularly　during　low　return　period　rainfall　events,　the　inclusion　of　both　stormwater　and　sewage　in　combined　sewer　networks　should　be　comprehensively　considered.