Steam　ejectors　are　regarded　as　a　promising　energy-saving　technology,　which　have　been　widely　used　in　many　industries.　The　aim　of　this　paper　is　to　optimize　the　geometrical　parameters　of　the　auxiliary　entraining　entrance　that　has　a　significant　influence　on　the　entrainment　performance.　In　this　study,　the　developed　auxiliary　entrainment　and　structure　optimization　make　good　use　of　the　low-pressure　potential　inside　the　throat　for　performance　improvement.　Moreover,　the　influence　of　auxiliary　entraining　entrance　geometric　parameters　on　internal　flow　fields　and　mass　flow　rate　have　been　obtained　numerically　and　analyzed　carefully,　and　the　special　internal　flow　characteristics　are　also　presented　and　discussed　in　detail　to　emphasize　the　role　of　auxiliary　entraining　entrance　geometric　parameters　in　determining　entrainment　performance.　The　results　reveal　that　the　major　influence　factors　of　entrainment　performance　are　the　effective　suction　pressure　area,　the　near-wall　mixed　steam　velocity　and　the　negative　affect　on　main　entraining　entrance.　And　there　are　an　optimum　geometrical　parameters　combination　of　the　auxiliary　entraining　entrance,　whose　opening　center　position　is　119mm,　opening　width　is　5　mm　and　opening　angle　is　90　degrees　for　the　given　ejector　and　operation　parameters,　with　a　maximum　entrainment　ratio　improvement　of　3.80%　comparing　with　that　of　the　conventional　designed　steam　ejector.　Furthermore,　the　auxiliary　entraining　entrance　can　be　designed　in　an　appropriate　range.