Objective To study the relation between competitive flow and graft flow in coronary artery bypass grafting. Methods Twelve adult healthy dogs （weighing 27. 62 ± 1. 63 kg） were anesthetized and received offpump coronary artery bypass grafting. During operation, flow meter was used to measure the degree of stenosis, and according to which four groups were classified. They were： non-stenosis group, 33% stenosis group, 50% stenosis group and 75 % stenosis group. Hemodynamic parameters including flow volume of graft, pulsatility indes （PI）, heart rate（HR） and mean arterial pressure（MAP） were recorded with or without competitive flow. Results When there was a competitive flow, the flow volume of graft in all four groups was less than the flow volume of graft which has not been affected by competitive flow. PI of non-stenosis group and 33% stenosis group was lower than normal PI. 50% stenosis group PI decreased from 8. 36±3. 52 to 3. 02±0. 94; 75% stenosis group PI was more than 5. Conclusion Competitive flow will restrain the graft flow. The position of graft anastomosis may be affected graft＇s patency.