Coastal　cities　face　severe　compound　flooding,　including　both　fluvial　flooding　and　pluvial　flooding.　Currently,　there　is　a　lack　of　comprehensive　methods　to　analyze　the　driving　factors　of　compound　flooding.　This　study　establishes　a　coupled　one-dimensional　and　two-dimensional　hydrodynamic　model.　Based　on　historical　data,　the　model　constructs　joint　probability　distributions　of　rainfall　and　tide　levels　with　different　return　periods　and　durations.　Using　the　results　from　the　coupled　model　under　various　design　scenarios,　the　study　proposes　an　impact　index　to　quantify　the　relative　contributions　of　rainfall　and　tide　level　to　flooding.　Additionally,　the　model　quantifies　the　interactions　between　fluvial　flooding　and　pluvial　flooding.　Taking　the　Shahe　River　basin　in　Guangzhou,　China,　as　a　case　study,　the　results　show　that　the　combination　of　the　copula　function　and　the　Kendall　return　period　method　is　effective　for　designing　hydrological　variable　combinations.　The　impact　degree　index　of　rainfall　on　flooding　varies　between　0.5　and　1,　with　the　minimum　at　24　h　duration,　indicating　that　the　compound　flooding　is　primarily　affected　by　rainfall,　and　the　influence　of　tide　level　is　most　significant　at　24　h　duration.　The　pluvial　flooding　caused　by　the　influence　of　river　water　level　on　the　drainage　outfalls　accounts　for　up　to　19.08　%　of　the　total　volume.　This　shows　that　fluvial　flooding　affects　the　seriousness　of　compound　flooding　by　influencing　the　water　levels　of　outfalls.　The　flood-prone　area　is　divided　into　different　regions　based　on　the　main　natural　factors　(rainfall　and　tide　level)　and　social　factors　(pipeline　network,　drainage　outfalls,　and　riverbank　defenses)　to　help　decision-makers　identify　the　causes　of　flooding　in　each　drainage　unit　and　better　formulate　targeted　disaster-reduction　strategies　to　improve　flood　control　capabilities.