Abstract： Objective:To investigate the relationship between the changes of cardiac vagus nerve function and postoperative atrial fibrillation(POAF)after off-pump coronary artery bypass grafting(OPCABG).Methods:This study was a retrospective case-control study.Clinical data of 737 patients with coronary atherosclerotic cardiovascular disease undergoing OPCABG were selected from the department of cardiovascular surgery in the General Hospital of North Theater from November 2020 to January 2022.There were 545 males and 192 females, aged(61.97±8.34)years old, ranging from 44 to 79 years old.After surgery, the Root mean square of sueeessive differenees between adjacent normal cycle(RMSSD)less than 15 ms indicated decreased vagal nerve function, and the patients were divided into the non-decreased vagal nervous system groupand the decreased vagal nervous system group.All patients received conventional treatment and OPCABG was selected.The incidence of atrial fibrillation and the perioperative trend of RMSSD were compared between the two groups.Results:The incidence of atrial fibrillation in the non-reduced group[31.2%(155/497)]was higher than that in the reduced group[21.3%(51/240)], and the difference was statistically significant( P<0.05).The postoperative RMSSD of the non-reduction group[(25.480±0.621)ms]was higher than that of the reduction group[(12.44±0.12)ms], and the difference was statistically significant( P<0.05). Conclusions:The relationship between the change of vagus nerve function and the occurrence of atrial fibrillation after OPCABG is non-linear, and patients with hypervagus or normal vagus after OPCABG are more likely to develop POAF.