This　paper　presents　an　investigation　combining　both　experiment　and　simulation　on　the　sole　impacts　of　the　injection　pressure　p(in)　on　the　inner　cavitation　process,　and　the　effects　of　the　cavitation　on　the　flow　capacity　of　the　nozzle.　An　optical　nozzle　is　designed　based　on　the　similarity　principle　of　amplification　in　an　equal　proportion,　and　both　the　structure　and　the　cavitation　number　are　similar　to　the　baseline　nozzle.　A　numerical　model　is　built　to　analyse　the　details　of　the　inner　flow.　The　results　show　that　cavitation　occurs　as　p(in)　increases,　and　a　bubble　ring　forms.　The　total　flow　process　is　divided　into　three　periods:　the　no-cavitation,　the　cavitation　developing　and　the　stable　cavitation　periods.　During　the　no-cavitation　period,　no　bubbles　occur,　and　the　discharge　coefficient　C-d　is　a　constant　and　determined　by　the　nozzle　structure.　During　the　cavitation　developing　period,　when　p(in)　rises,　the　area　of　the　bubble　ring　increases,　but　C-d　decreases　and　is　governed　by　f　the　cavitation　number　CN　and　the　cavitation　area　coefficient　K-A.　During　the　stable　cavitation　period,　at　the　inlet　the　bubble　ring　reaches　the　maximum　then　becomes　stable;　C-d　is　determined　only　by　CN,　and　infinitely　close　to　a　constant　as　p(in)　increases.　(C)　2016　Elsevier　Ltd.　All　rights　reserved.