Submerged　fuel　jet　occurs　in　the　nozzle　chamber　for　a　high-pressure　common　rail　diesel　fuel　system.　Cavitation　is　often　caused　during　the　submerged　fuel　jet　due　to　great　pressure　difference　of　the　fuel　flow.A　test　rig　with　a　circular　nozzle　was　built　in　order　to　investigate　influences　of　the　inlet　and　back　pressures　on　the　flow　characteristics　of　the　submerged　fuel　jet.　During　the　experiment,　the　cavitation　process　at　the　nozzle　outlet　was　directly　detected　by　a　videoscope,　and　the　impingement　force　was　obtained　by　jetting　the　fuel　onto　a　target　plate.The　experimental　results　show　that　the　cavitation　incepts　in　the　circular　nozzle　and　then　develops　to　the　outlet　of　the　nozzle.　According　to　the　development　of　the　cavitation　in　the　nozzle,　the　submerged　fuel　jet　experiences　into　two　periods.　During　the　inner-cavitation　period　,　the　cavitation　does　not　reach　the　nozzle　outlet　yet,　the　impingement　force　increases　with　the　decrease　of　the　back　pressure,　and　reaches　its　maximum　when　the　cavitation　occurs　just　at　the　nozzle　outlet.　During　the　cavitation-jet　period　,　the　cavitation　reaches　the　nozzle　outlet　and　enters　into　the　background　fuel　field　to　form　a　cavitation　jet,　the　impingement　force　begins　to　drop　until　reaches　a　stable　value　with　the　decrease　of　the　back　pressure.Moreover,　as　the　inlet　pressure　increases,　both　the　maximum　impingement　forces　and　the　average　stable　impingement　forces　first　increase　and　then　become　constant　at　last.　©　2018,　Editorial　Office　of　the　Transaction　of　CSICE.　All　right　reserved.