The　high-speed　flow　of　internal　fuel　in　diesel　fuel　injector　is　easy　to　cause　cavitation　inside　the　nozzle,　which　affects　the　flow　of　fuel.　It　is　very　important　to　study　the　cavitation　process　of　fuel　in　the　nozzle.　The　flow　characteristics　of　the　nozzle　under　different　inlet　and　outlet　pressures　is　studied　by　experiments　on　the　scale-enlarged　visualization　test　bench.　The　experimental　results　show　that　the　inlet　pressure　is　constant,　with　the　decrease　in　the　outlet　pressure,　1)　during　the　no　cavitation　period,　the　discharge　coefficient　is　basically　unchanged;　2)　during　the　cavitation　developing　period,　cavitation　becomes　stronger　and　develops　from　the　entrance　of　the　nozzle　to　the　outlet,　the　mass　flow　rate　continues　to　increase　and　the　discharge　coefficient　decreases;　3)　during　the　cavitation　saturation　period,　the　mass　flow　rate　maintains　stable　but　the　discharge　coefficient　continues　decreasing.　The　inlet　pressure　of　the　nozzle　does　not　affect　the　critical　cavitation　number　of　cavitation　inception　and　cavitation　saturation.　The　diameter　of　the　nozzle　does　not　affect　the　point　of　cavitation　inception,　but　the　point　of　cavitation　saturation;　as　the　diameter　of　the　nozzle　is　larger,　the　more　difficult　it　is　to　achieve　the　cavitation　saturation,　and　the　smaller　of　the　critical　cavitation　number.　The　length　of　the　nozzle　affects　the　point　of　cavitation　inception　and　cavitation　saturation;　the　length　of　the　nozzle　is　longer,　the　more　difficult　it　is　to　occur　cavitation　and　to　achieve　cavitation　saturation,　the　critical　cavitation　numbers　of　both　the　cavitation　inception　and　the　cavitation　saturation　are　smaller.　©　2016,　Editorial　Board　of　Acta　Armamentarii.　All　right　reserved.