When　the　ejector　was　applied　to　the　natural　gas　exploration　and　sea　industries,　the　ejector　always　operated　on　the　two　phase　operation,　because　of　the　primary　fluid　or　the　induced　fluid　usually　companying　some　water　inside.　In　the　present　study,　an　experimental　investigation　was　carried　out　to　study　the　ejector　performance　on　the　two　phase　operation,　when　the　water　was　injected　into　the　primary　fluid.　The　results　show　that:　two　phase　operation　has　little　effect　on　the　entrainment　ratio　with　the　difference　less　than　2.7%,　when　the　ejector　was　at　critical　mode.　When　the　ejector　was　at　sub-critical　mode,　the　entrainment　ratio　decreased,　with　the　large　deviation　17%.