Using　the　method　combining　experiments　and　numerical　simulations,　the　dynamic　behavior　of　explosion　bubbles　for　the　cylindrical　charges　with　different　length-diameter　ratios　(L/D)　under　fixed　square　plates　was　studied.　Explosion　tests　of　TNT　explosives　with　the　mass　of　2.5g　and　L/D　of　1:1　and　2:1　under　a　fixed　square　plate　was　carried　out,　and　the　evolution　of　explosive　bubbles　was　recorded　by　the　high-speed　camera.　ABAQUS　software　was　used　to　numerically　simulate　the　underwater　explosion　bubble　evolution　process　of　cylindrical　charges　with　L/D　of　5:1,　10:1,　and　20:1　under　vertical　and　horizontal　settings.　The　results　show　that　there　is　no　obvious　difference　between　the　explosion　of　2.5g　TNT　explosives　with　a　L/D　of　1:1　and　2:1　under　the　board.　When　the　explosives　are　placed　vertically,　the　difference　in　the　initial　shape　of　the　explosion　bubble　caused　by　different　L/D　of　the　explosives　will　be　quickly　eliminated　during　the　evolution　of　the　bubble.　Moreover,　the　L/D　and　the　starting　position　have　effects　on　the　water　jet.　When　the　explosives　are　placed　horizontally,　the　symmetry　of　the　bubble　and　the　shape　of　the　water　jet　will　be　affected　by　the　location　of　the　initiation　point.　To　be　specific,　for　the　detonation　from　the　end　face,　there　is　a　slight　asymmetry　in　the　process　of　the　bubble　expansion,　and　the　jet　is　offset　in　the　direction　of　the　starting　point.　Moreover,　the　larger　the　L/D　of　the　explosives,　the　wider　the　water　jet　in　the　explosion　bubble,　and　the　smaller　the　load　of　the　water　jet.　For　the　detonation　from　the　center,　the　explosive　bubble　forms　a　vertical　water　jet　without　offset.　©　2024　China　Ordnance　Industry　Corporation.　All　rights　reserved.