The　current　research　on　the　cavitation　phenomenon　in　the　underwater　explosion　process　is　focused　on　the　shock　wave　phase.　In　this　study,　it　was　found　that　there　was　also　significant　cavitation　during　bubble　pulsation.　Underwater　explosion　experiments　were　carried　out　at　the　bottom　of　a　sheet　using　2.5　g　of　TNT,　which　also　showed　that:　(a)　Cavitation　lasts　for　the　same　duration　as　the　bubble　contraction　time,　(b)　A　cavitation　closure　pressure,　the　peak　of　which　is　greater　than　the　bubble　pulsation　pressure,　is　produced　by　the　closing　of　the　cavitation　zone.　A　tensile　cut-off　model　was　introduced　to　simulate　the　cavitation　phenomenon　during　bubble　pulsation,　and　the　formation　mechanism　was　investigated.　The　numerical　simulation　results　show　that:　(a)　The　cavitation　phenomenon　is　visible　when　the　sheet　above　the　explosive　and　the　explosion　distance　are　between　0.93　and　1.17　times　the　radius　of　the　largest　bubble,　or　between　0.69　and　1.85　times　the　maximum　radius　of　the　bubble　when　the　sheet　below　the　explosive,　(b)　The　cavitation　region　and　cavitation　closure　pressure　increase　and　decrease　with　increasing　explosion　distance,　peaking　at　a　value　close　to　one　times　the　theoretical　maximum　bubble　radius,　and　(c)　The　cavitation　zone　shrinks　and　the　cavitation　closing　pressure　drops　as　sheet　thickness　increases.