Objective To investigate the use of intraoperative transit time flow measurement （TTFM） to accuratelyevaluate graft patency during sequential coronary artery bypass grafting （CABG）. Methods Clinical data of 131 patientsundergoing sequential off-pump coronary artery bypass grafting （OPCAB） with the great saphenous vein （with or without internal mammary artery） as graft vessels in Beijing Anzhen Hospital from April 2012 to January 2013 were retrospectivelyanalyzed. There were 92 male and 39 female patients with their age of 61.35±8.24 years. During the operation，2 methods were used to measure mean blood flow volume，pulsatility index （PI） and diastolic filling （DF） of the graft vessels. For thenon-blocking method，blood flow in graft vessels was maintained，and TTFM was applied 2 cm proximal to the anastomoticsite in graft vessels to record above parameters. For the blocking method，blood flow in graft vessels was temporally blockedby clipping distal graft vessels with an atraumatic bulldog clamp，and TTFM was applied 2 cm proximal to the anastomotic site in graft vessels to record above parameters. Results Blood flow volumes of the diagonal branch （27.43±15.22 ml/minvs. 59.28±30.13 ml/min），obtuse marginal branch （26.14±19.74 ml/min vs. 47.19±24.27 ml/min） and posterior left ventr-icular branch （19.16±8.92 ml/min vs. 38.83±20.11 ml/min） measured by the blocking method were significantly smallerthan those measured by the non-blocking method （P＜0.05） . PI values of the diagonal branch （2.93±1.30 vs. 2.31±0.91），obtuse marginal branch （2.62±1.17 vs. 2.01±0.87） and posterior left ventricular branch （2.33±0.92 vs. 1.80±0.73） meas-ured by the blocking method were significantly higher than those measured by the non-blocking method （P＜0.05）. There was no statistical difference in DF values measured by 2 methods at respective anastomotic sites，and all DF values were higher than 50%. Non-blocking method identified 1 anastomotic site and blocking method identified 3 anastomotic sites that were not patent，and these anastomotic sites became patent after graft reconstruction. Conclusion Blood flow velocity of sequential grafts is higher than that of single grafts，indicating that sequential grafts have the advantages of high blood flow volume and low risk of thrombosis. Blocking method can more accurately evaluate graft patency at the anastomotic sites and sensitively identify graft vessels that are not patent，which is helpful for anastomotic site reconstruction in time and enhancement of successful rate of CABG.