Objective: To compare the blood lfow of left internal mammary artery (LIMA) graft vessel between minimally invasive direct coronary artery bypass (MIDCAB) and traditional median sternotomyin off-pump coronary artery bypass (Traditional OPCAB) by transit-time lfow meter (TTFM). Methods: We retrospectively studied 300 patients who received OPCAB in our hospital from 2013-01 to 2015-07, all patients had LIMA to left anterior descending coronary artery (LAD) anastomosis. The patients were divided into 2 groups: MIDCAB group, n=70 and Traditional OPCAB group,n=230. Intra-operative blood lfow in graft vessel was measured by transit-time lfow meter. Pre- and post-operative indexes and the mean lfow (MF), pulsatile index (PI), diastolic fraction (DF) of LIMA graft were compared between 2 groups. Results: The following indexes in Traditional OPCAB group and MIDCAB group were as below: intra-operative transfusion was (3.00±5.42) U vs (1.06±2.17) U, post-operative peak value of cTnI was (2.84±9.93) ng/ml vs (0.69±1.74) ng/ml, mechanical ventilation time was (27.9±66.9) h vs (14.2±20.8) h and ICU stay time was (64.1±89.6) h vs (35.2±39.2) h, allP<0.05; while for the graft from LIMA to LAD, MF was (29.45±18.19) ml/min vs (29.04±15.85) ml/min, PI was (2.68±1.19) vs (2.44±0.84) and DF was (71.47±11.12) % vs (70.25±11.30) %, allP>0.05. Conclusion: With LIMA to LAD graft, MIDCAB may achieve the same effect as traditional OPCAB, the early post-operative anastomosis has been reliable.