To　investigate　the　influence　of　grid　size　and　water　size　on　the　accuracy　of　three-dimentional　(3D)　numerical　simulation　of　underwater　explosion,　and　to　give　the　parameter　settings　that　can　balance　the　accuracy　and　efficiency　of　3D　numerical　simulation　of　underwater　explosion,　this　paper　is　based　on　the　LS-DYNA　3D　free　field　model　of　underwater　explosion,　using　the　peak　of　underwater　explosion　shock　wave,　bubble　pulsation　characteristics　and　water　motion　characteristics　as　indicators,　in　50　-　300　kg　explosion　equivalent,　and　analyzed　the　influence　of　grid　size　and　water　size　on　the　accuracy　of　numerical　simulation　respectively.　Results　show　that　the　grid　size　is　not　more　than　1　times　the　radius　of　the　charge,　the　distance　from　the　center　of　the　explosive　to　the　boundary　of　the　water　is　not　less　than　4　times　the　maximum　expansion　radius　of　the　bubble,　and　the　software　can　be　more　accurate　simulation　of　underwater　explosion　shock　wave　and　the　first　bubble　pulsation　of　the　whole　process.　Considering　the　calculation　accuracy　and　efficiency,　it　is　recommended　that　the　grid　size　should　not　be　larger　than　1　times　the　radius　of　the　charge　and　the　distance　from　the　center　of　the　charge　to　the　water　boundary　should　not　be　less　than　4　times　the　maximum　expansion　radius　of　the　bubble　when　the　numerical　simulation　of　underwater　explosion　is　carried　out.　©　2023　Beijing　University　of　Technology.　All　rights　reserved.