In　order　to　clarify　the　influence　of　graft-host　diameter　ratios　on　the　flow　patterns　and　the　wall　shear　stress　in　coronary　artery　bypass　graft　(CABC),　three　CABG　models　with　the　graft　diameter　smaller　than,　equal　to　and　larger　than　that　of　the　coronary　artery,　were　constructed.　The　physiologically　pulsatile　blood　flows　in　these　three　models　were　simulated　with　finite　element　method.　The　temporal-spatial　distributions　of　flow　patterns,　wall　shear　stresses,　and　wall　shear　stress　based　parameters　were　depicted　and　compared.　The　results　showed　that　the　large　model　features　with　relatively　large　positive　longitudinal　velocity,　uniform　and　large　wall　shear　stresses,　and　small　wall　shear　stress　gradients.　The　hemodynamics　in　the　large　model　was　improved　to　some　extent.　Larger　or　isodiametric　graft　is　favorable　in　the　CABG　surgical　application.　However,　no　distinct　difference　of　wall　shear　stress　based　temporal　parameters　was　found　between　all　the　three　models.　Alternative　anastomotic　designs　are　necessary　for　the　improvement　of　CABG　patency　rates.