In　this　study,　Computational　Fluid　Dynamics　(CFD)　technique　is　employed　to　investigate　the　effects　of　two　important　ejector　geometry　parameters:　the　primary　Nozzle　Exit　Position　(NXP)　and　the　mixing　section　converging　angle　theta,　on　its　performance.　A　CFD　model　is　firstly　established　and　calibrated　by　actual　experimental　data,　and　then　used　to　create　95　different　ejector　geometries　and　tested　under　different　working　conditions.　From　210　testing　results,　it　is　found　that　the　optimum　NXP　is　not　only　proportional　to　the　mixing　section　throat　diameter,　but　also　increases　as　the　primary　flow　pressure　rises.　On　the　other　hand,　the　ejector　performance　is　very　sensitive　to　theta　especially　near　the　optimum　working　point.　The　entrainment　ratio　can　vary　as　much　as　26.6%　by　changing　theta.　A　relatively　bigger　theta　is　required　to　better　maximize　the　ejector　performance　when　the　primary　flow　pressure　rises.　The　significance　of　the　study　is　that　these　findings　can　be　used　to　guide　the　adjustment　of　NXP　and　theta　in　order　to　obtain　the　best　ejector　system　performance　when　the　operating　conditions　are　different　from　the　on-design　conditions.　(C)　2008　Elsevier　Ltd.　All　rights　reserved.