Objective: To investigate and analyze the relationship between intraoperative graft flow measurements and the early mid-term outcomes after off-pump coronary artery bypass grafting (OPCAB). Methods: Patients who underwent isolated OPCAB in the Department of Cardiac Surgery of Peking University People’s Hospital from January 2013 to June 2016 were included. Perioperative characteristics, graft flow measurements and postoperative follow-up outcomes were retrospectively collected. Comparison was made between flow measurements of grafts and the early mid-term outcomes. Flow measurements of grafts included the mean flow (MF) and the pulsatility index (PI). The early outcomes included peri-operative myocardial infarction (PMI), use of an intra-aortic balloon pump (IABP), reoperation for all causes, new-onset atrial fibrillation and in-hospital or 30-day mortality. Results: A total of 463 patients were included in the study. Mean age was (62.80±8.36) years, and 24.8% were females. The total number of grafts was 1 435, which averaged 3.10 grafts per patient. The MF and PI were separately (32.34±14.45) mL/min and 2.87±0.92. Of all the patients, 23(5%) had PMI, and 11 used IABP. Observed in-hospital or 30-day mortality was 0.86% (4 patients). Compared with non-PMI group, the MF was lower and the PI was higher in the PMI group (P<0.05). However, the differences of other early outcomes had no statistical significance between the PMI group and the non-PMI group. The lower MF (Wald=5.684, P=0.017, 95%CI: 0.894-0.989) and the higher PI (Wald=9.040, P=0.003, 95%CI: 1.252-2.903)were risk factors of PMI in multivariable Logistic regression modeling. The longest follow-up time was 37 months, and 7 patients died. The differences of graft flow measurements between the surviving group and the non-survivors had no statistical significance, but overall mid-term survival was lower in patients with poor left internal mammary artery (LIMA) to left anterior descending artery (LAD) graft flow (MF<10 mL/min; OR=9.6, P<0.05). Conclusion: Intraoperative graft flow parameters during OPCAB can predict the early mid-term outcomes. The lower MF and the higher PI should increase the rate of PMI. A lower flow of LIMA to LAD graft (<10 mL/min) should increase the rate of midterm mortality, but further research will be needed to confirm and explore the findings.