A　numerical　study　of　supercritical　CO2　two-phase　flow　in　the　ejector　was　carried　out　by　computational　fluid　dynamics　(CFD)　methods.　Through　the　comparison　of　simulation　results　and　available　experimental　data　in　the　literature,　the　accuracy　of　the　three-dimensional　CFD　model　was　verified.　A　comparison　of　the　effects　of　four　turbulence　models　on　the　simulation　calculation　results　was　also　presented.　The　distributions　of　pressure,　velocity,　two-phase　volume　fraction,　shock　wave　and　exergy　flux　inside　the　ejector　were　analyzed.　The　effects　of　the　mixing　section　geometry　on　the　performance　of　the　ejector　were　obtained.　Then,　the　entrained　performance　of　the　ejector　was　investigated　by　changing　the　area　ratio　between　the　constant-area　mixing　chamber　and　the　outlet　of　the　motive　nozzle　(AR)　and　the　ratio　between　the　length　and　the　diameter　of　the　constant-area　mixing　chamber　(LDR).　Finally,　the　optimum　AR　and　LDR　were　determined　to　be　8.3　and　8.1,　respectively　based　on　the　maximum　entrained　ratio　and　the　minimum　exergy　destruction.　Through　optimizing　the　mixing　chamber　geometry,　the　minimum　total　exergy　destruction　and　the　maximum　mass　entrainment　ratio　(MER)　of　the　ejector　can　attain　0.33　J/(kg　center　dot　K)　and　0.698　respectively.