Clinically,　fractional　flow　reserve　(FFR)-guided　coronary　artery　bypass　grafting　(CABG)　is　more　effective　than　CABG　guided　by　coronary　angiography　alone.　However,　no　scholars　have　explained　the　mechanism　from　the　perspective　of　hemodynamics.　Two　patients　were　clinically　selected;　their　angiography　showed　70%　coronary　stenosis,　and　the　FFRs　were　0.7　(patient　1)　and　0.95　(patient　2).　The　FFR　non-invasive　computational　model　of　the　two　patients　was　constructed　by　a　0-3D　coupled　multiscaled　model,　in　order　to　verify　that　the　model　can　accurately　calculate　the　FFR　results.　Virtual　bypass　surgery　was　performed　on　these　two　stenoses,　and　a　CABG　multiscaled　model　was　constructed.　The　flow　rate　of　the　graft　and　the　stenosis　coronary　artery,　as　well　as　the　wall　shear　stress　(WSS)　and　the　oscillatory　shear　index　(OSI)　in　the　graft　were　calculated.　The　non-invasive　calculation　results　of　FFR　are　0.67　and　0.91,　which　are　close　to　the　clinical　results,　which　proves　that　our　model　is　accurate.　According　to　the　CABG　model,　the　flow　ratios　of　the　stenosis　coronary　artery　to　the　graft　of　patient　1　and　patient　2　were　0.12　and　0.42,　respectively.　The　time-average　wall　shear　stress　(TAWSS)　results　of　patient　1　and　patient　2　grafts　were　2.09　and　2.16　Pa,　respectively,　and　WSS　showed　uniform　distribution　on　the　grafts.　The　OSI　results　of　patients　1　and　2　grafts　were　0.0375　and　0.1264,　respectively,　and　a　significantly　high　OSI　region　appeared　at　the　anastomosis　of　patient　2.　The　FFR　value　of　the　stenosis　should　be　considered　when　performing　bypass　surgery.　When　the　stenosis　of　high　FFR　values　is　grafted,　a　high　OSI　region　is　created　at　the　graft,　especially　at　the　anastomosis.　In　the　long　term,　this　can　cause　anastomotic　blockage　and　graft　failure.