Study　region:　The　study　area　is　the　western　part　of　the　Macau　Peninsula　in　China,　with　an　area　of　4.06　km2.　Study　focus:　This　study　developed　a　coupled　hydrological-hydraulic　model　that　simulates　the　twodimensional　(2D)　surface　flow　and　one-dimensional　(1D)　drain　pipe　flow　of　compound　inundation.　The　model　was　applied　to　Macau,　China,　as　a　study　area,　and　the　typhoon　Mangkhut　in　2018　was　used　as　a　case　study　to　validate　the　model＇s　performance.　Simulating　compound　inundation　scenarios　of　extreme　rainfall　and　astronomical　tide　and　exploring　the　influence　of　astronomical　tide　on　coastal　urban　inundation.　New　hydrological　insights　for　the　region:　Urban　flood　disasters　are　profoundly　influenced　by　tidal　levels,　albeit　the　height　of　tides　alone　does　not　solely　exacerbate　the　phenomenon.　Rather,　the　phase　of　astronomical　tides　during　rainfall　also　plays　a　crucial　role　in　determining　the　severity　of　urban　flooding.　This　research　has　revealed　that　when　rainfall　synchronizes　with　the　recession　phase　of　the　spring　tide,　urban　flooding　conditions　become　acute,　17.66　%　increase　in　total　surface　water　volume　for　the　scenario　with　the　highest　tidal　level　impact　compared　to　the　scenario　with　the　lowest　tidal　level　impact.　This　paper　presents　the　response　of　coastal　cities　to　the　flooding　process　under　different　combined　rainstorm-astronomical　tide　scenarios,　to　provide　scientific　guidance　for　disaster　preparedness　planning　in　coastal　areas,　and　to　improve　the　resilience　of　disasters.