It　is　crucial　to　enhance　the　entrainment　performance　of　steam　ejectors　which　operate　under　double-critical　conditions　to　widen　their　application　in　industries.　In　this　paper,　combined　auxiliary　entrainment　technical　approach　is　proposed　and　corresponding　geometric　structure　optimization　has　implemented　systematically,　for　a　better　use　of　the　inside　low-pressure　potential　thus　greatly　improving　the　entrainment　performance　of　the　steam　ejector　under　double-critical　conditions.　Moreover,　a　comprehensive　analysis　and　discussion　of　the　influence　of　the　geometrical　parameters　on　the　auxiliary　entrainment　performance　has　been　obtained　from　mass　flow　rate,　pressure　field　and　special　internal　flow　characteristics.　The　results　reveal　that　the　combined　auxiliary　entrainment　is　the　best　choice　for　the　given　steam　ejector　operating　under　the　double-critical　conditions,　and　the　optimum　geometrical　parameters　of　throat　auxiliary　entraining　entrance　are　same　as　the　designed　condition　and　remain　unchanged.　For　the　diffuser　auxiliary　entraining　entrance,　the　opening　starting　position　X-s　could　be　set　at　the　entrance　of　the　diffuser　identically,　the　opening　angle　could　be　chosen　as　a　common　range　R　e　from　75　degrees　to　105　degrees.　However,　the　optimum　opening　width　d　increases　with　the　decrease　of　back　pressure　p(c).　In　general,　there　is　an　optimum　geometrical　parameters　combination　that　the　entrainment　performance　can　achieve　its　maximum　value　for　each　p(c).　The　smaller　the　p(c),　the　bigger　the　entrainment　ratio　improvement,　as　large　as　34.8%　for　p(c)　of　32　kPa.