The　common-rail　injector　precisely　controls　the　fuel　injection　by　adjusting　the　pressure　of　its　control　chamber　to　change　the　submerged　jet　and　the　force　on　the　needle.　Therefore,　study　of　the　submerged　jet　of　the　control　chamber　is　great　significance　for　diesel　fuel　flow　characteristics　and　injection　control　accuracy　in　injector.　This　work　designs　a　visualization　test　rig　to　test　the　diesel　fuel　submerged　jet　as　well　as　the　impingent　force　under　conditions　of　varied　inlet/outlet　pressures.　The　test　results　show　that　the　submerged　jet　of　the　control　chamber　is　relative　with　the　inner　flow　of　the　cylindrical　orifice　in　front　of　the　control　chamber.　For　a　given　constant　inlet　pressure,　as　the　back　pressure　decreases,　the　inner　flow　of　the　cylindrical　orifice　first　is　laminar,　and　then　becomes　turbulent;　in　addition,　cavitation　occurs.　This　inner　cavitation　turbulence　flow　of　the　cylindrical　orifice　induces　the　changing　of　the　impingent　force.　The　developing　process　of　the　impingent　force　is　divided　into　three　periods:　1)　rising　period;　2)　fluctuation　period;　3)　rising　again　period.　©　2019,　Science　Press.　All　right　reserved.