The　submerged　jet　is　a　common　phenomenon　in　a　fluid　machinery　that　controls　fluid　flow　by　adjusting　the　back　pressure　with　constant　inlet　pressure　during　the　energy　transforming　process,　and　it　has　different　characteristic　with　that　by　adjusting　the　total　differential　pressure.　This　work　investigates　the　submerged　cavitation　jet　flow　inside　a　narrow　cylindrical　orifice　under　condition　of　varied　back　pressure.　An　optical　test　rig　is　to　examine　the　submerged　jet,　and　a　three-dimension　numerical　model　is　to　investigate　the　details.　The　results　reveal　that　for　constant　inlet　pressure,　as　the　back　pressure　declines,　cavitation　jet　occurs.　The　development　process　of　the　impingement　force　is　divided　into　three　periods.　Period　I,　the　impingent　force　monotonically　increases.　Period　II,　from　the　choking　point　to　the　cavitation　jet　starting　point,　the　impingent　force　slightly　decreases.　Period　III　the　impingent　force　rises　again.　During　the　choking　period,　the　input　energy　is　unchanged,　but　the　impact　force　declines.　This　is　because　the　turbulence　kinetic　energy　increases　resulting　in　pressure　energy　decrease.　For　given　pressure　boundaries,　the　impingent　force　rises　as　the　standoff　distance　of　the　target　plate　increases,　and　the　standoff　has　fewer　influences　on　the　impingent　force　when　the　target　plate　is　farther.　(C)　2018　Elsevier　Ltd.　All　rights　reserved.