The　geometric　factors　have　prominent　impacts　on　the　success　rate　of　coronary　artery　bypass　graft　(CABG).　In　order　to　clarify　how　to　choose　suitable　graft-host　diameter　ratio　and　junction　angle,　ANSYS9.0　was　used　to　simulate　CABG,　then　response　surface　methodology　was　applied　to　construct　mathematical　model,　finally　theory　of　optimization　was　performed　to　determine　the　optimum　graft-host　diameter　ratio　and　junction　angle　which　could　make　the　main　factor　influencing　the　success　rate　of　CABG,　i.e.　wall　shear　stress　gradients,　smallest.　The　result　indicates　that　the　model　of　large　graft-host　diameter　ratio　and　small　junction　angle　has　better　hemodynamics.　It　can　be　concluded　that　adopting　large　graft-host　diameter　ratio　and　small　junction　angle　with　the　help　of　clinical　experiences　is　advisable　in　CABG　surgery.