The　hydraulic　concrete　structures　were　partially　or　fully　in　direct　contact　with　water　during　the　service　life.　The　mechanical　properties　of　saturated　concrete　are　different　from　dry　concrete　because　of　the　presence　of　water.　To　investigate　the　underwater　blast　resistance　mechanism　of　saturated　concrete,　saturated　concrete　slabs　were　first　tested　in　underwater　explosion　experiments　with　different　TNT　masses　of　2.5　g,　5　g,　and　10　g.　The　experimental　results　showed　that　the　crater　on　the　front　of　the　concrete　slab　was　smaller　than　those　on　the　back　and　the　size　of　the　crater　increased　with　increasing　mass　of　TNT.　Numerical　simulations　were　conducted　and　material　param-eters　were　determined　based　on　additional　tests:　The　damage　model　under　different　stress　states　was　proposed　by　repeated　loading　and　unloading　tests　in　tension　and　compression　under　different　confining　pressures.　The　damage　model　was　then　embedded　into　the　Holmquist-Johnson-Cook　(HJC)　model.　Quasi-static　and　dynamic　compression　experiments　were　conducted　to　determine　the　material　parameters　of　the　saturated　concrete.　A　three-dimensional　fluid-solid　coupling　numerical　model　in　ABAQUS　was　proposed　for　simulating　the　underwater　explosion　and　its　interaction　with　the　saturated　concrete　slab.　Finally,　the　mechanisms　that　produce　differences　in　the　damage　pattern　of　concrete　slabs　at　different　explosive　masses　are　revealed.