The　cavitation　phenomenon　caused　by　near-field　underwater　explosion　imposes　a　secondary　loading　on　ship　structures.　Studying　the　cavitation　effects　of　plates　during　underwater　explosions　has　implications　for　ship　protection　since　plate　is　a　typical　structure　of　ships.　This　paper　experimentally　investigated　the　behavior　of　fixed　square　plates　subjected　to　near-field　underwater　explosions.　Experimental　results　indicated　that　cavitation　existed　in　both　shockwave　and　bubble　pulsation　stages;　and　the　cavitation　closure　load　at　bubble　pulsation　stage　was　measured.　To　further　investigate　the　cavitation　phenomenon　and　the　load　characteristics　at　the　bubble　pulsation　stage,　finite　element　models　were　developed.　The　numerical　results　show　that　cavitation　will　increase　the　bubble　load　impulse　by　47　%　under　specific　conditions.　These　models　were　then　used　to　investigate　the　influence　of　the　stand-off　distance　and　charge　weight　on　cavitation　area　and　load　characteristics.　An　empirical　formula　was　finally　proposed　to　predict　the　coupled　impulse　of　cavitation　closure,　bubble　pulsation　and　water　jet.　This　research　has　practical　guidelines　for　the　protection　design　of　ship　structures.