Background: Diabetic cardiomyopathy (DCM) is a serious complication of Obesity with type 2 diabetes. Bariatric surgery can effectively improve DCM; however, the underlying mechanisms remain elusive. Our objective was to investigate the effect and potential mechanisms of duode-nal-jejunal bypass (DJB) on oxidative stress in the heart. Methods: DJB was performed on DCM rats, and high glucose (HG) and palmitate (PA) were used to simulate DCM in H9C2 cells in vitro. AMPK agonists and inhibitors were used to verify the role of the AMPK pathway. Serum from different groups of rats was used to verify that the im-provement in DCM after DJB surgery was not strictly owing to improvement in blood glucose levels and connect the experiments in vivo and in vitro. Results: DJB surgery effectively improved oxidative stress and increased expression of the AMPK pathway, p-eNOS/eNOS, NRF2, HO-1, and SOD2 in terms of protein and mRNA in the heart of DCM rats. Compared to H9C2 cells in the HG+PA environment alone, the addition of either AMPK agonists or serum from DJB rats increased the expression of the AMPK pathway, p-eNOS/eNOS, NRF2, HO-1, and SOD2 in terms of protein and mRNA and decreased the content of ROS, but this improvement was almost eliminated by the addition of AMPK inhibitors. Conclusions: Therefore, DJB surgery can improve oxidative stress in the heart of DCM rats, which may be achieved by activating the AMPK pathway, thereby increasing the phosphorylation level of eNOS, increasing NO and reducing ROS production, and improving the antioxidant system and not solely the improvement of blood glucose.