Diabetes mellitus (DM) is an independent risk factor for postoperative neurocognitive disorders (PND), especially postoperative delirium (POD). A systematic review analyzed 182 studies from databases such as PubMed and the Cochrane Library up to November 2024. DM increases the risk of PND, with studies showing a 1.84-fold higher risk of postoperative cognitive dysfunction (POCD) in diabetic patients. Major mechanisms include cerebral vascular damage, impaired glucose metabolism, inflammation, and oxidative stress. Research is led by countries such as China, the USA and Germany. By 2045, DM is expected to affect more than 783 million people. Further research is needed to elucidate causal mechanisms and develop targeted interventions to reduce risk in diabetics undergoing surgery.