The　nozzle,　which　is　the　load　to　the　pump　and　converts　pressure　energy　into　kinetic　energy,　is　one　of　very　important　parts　of　water　jet　system.　Under　different　conditions,　the　nozzle　energy　conversion　efficiency　is　different,　resulting　in　the　effect　of　system　efficiency.　Due　to　the　cause　of　formation,　the　energy　loss　of　a　nozzle　is　classified　as　feature　energy　loss　and　cavitation　energy　ones.　Based　on　the　flow　characteristics,　the　influence　factors　and　the　relation　with　flow　coefficient　are　investigated.　Experiments　are　carried　out　to　study　the　flow　characteristics　of　cylinder　nozzles,　cone　nozzles　and　cosine　nozzles　and,　the　effects　of　the　inlet/outlet　conditions　and　the　nozzle　features　are　addressed.　Comparison　analyses　have　been　made　on　the　feature　and　cavitation　energy　loss　of　the　three　nozzles.　The　results　show　that　the　inlet　conditions　greatly　influence　the　cavitation　energy　loss　and　have　little　effects　on　feature　ones,　and　that　the　nozzle　features　significantly　affected　both　kinds　of　energy　losses　and　they　tend　to　be　smaller　when　the　inner　surface　is　closer　to　streamline.　The　related　conclusions　provide　a　basis　for　the　nozzle　optimal　design　and　the　improvement　of　the　efficiency　of　water　jet　system.　©　2013　Journal　of　Mechanical　Engineering.