Objective: To explore influence of exercise on cardiac autonomic nerve function in patients undergoing coronary artery bypass grafting (CABG) and its clinical significance. Methods: A total of 53 patients with coronary heart disease undergoing CABG were randomly divided into routine treatment group (n=25) and rehabilitation group (n=28, received exercise training based on routine treatment). Changes of autonomic nerve function before, second and eighth week after CABG were analyzed in two groups using time domain indexes of heart rate variability (HRV) by ambulatory electrocardiography, including standard deviation of normal to normal RR intervals calculated over the 24 h period (SDNN), standard deviation of normal to normal RR intervals in all 5 min segments of the entire recording (SDANN), root-mean square of differences between successive normal to normal intervals (rMSSD) and adjacent normal RR interval difference > 50ms stroke accounted for a percentage of 24h total RR interval (PNN50). Results: Compared with before CABG, there were significant decrease in SDNN, SDANN, RMSSD and PNN50 in both groups two weeks after CABG (P<0.05~0.01); eight weeks after CABG, above indexes recovered to levels before CABG in routine treatment group[SDNN （113.6±29.4）vs.（116.7±24.7）, SDANN（112.2±32.1）vs.（113.6±28.6）, rMSSD（21.9±8.2） vs.（23.2±7.1）, and PNN50 （7.5±4.2）vs.（8.2±3.7）] , P>0.05 all; Compared with before CABG, there were significant improvements in SDNN [(114.7±25.2) ms vs. (132.6±30.6) ms], SDANN [(111.6±23.5) ms vs. (129.2±30.8) ms], rMSSD [(24.2±8.7) ms vs. (29.9±7.5) ms] and PNN50 [(7.8±2.2) ms vs. (9.5±2.3) ms], and there were significant improvement than those of routine treatment group [SDNN （132.6±30.6）vs.（113.6±29.4）, SDANN（129.2±30.8）vs.（112.2±32.1）, rMSSD（29.9±7.5）vs.（21.9±8.2）and PNN50 （9.5±2.3）vs.（7.5±4.2）] eight weeks after CABG in rehabilitation group, P<0.05 all. Conclusion: All HRV indexes significantly decrease on two weeks after CABG in both groups, suggesting that CABG can damage cardiac autonomic nerve system. These indexes of rehabilitation group were more improvement than those of routine treatment group, suggesting exercise training can more significantly improve cardiac autonomic nerve function after CABG.