Objective To investigate the effect of preoperative sleep quality on the development of postoperative delirium (POD) in elderly patients undergoing thoracic surgery and the risk factors associated with the development of postoperative delirium through multivariate logistic regression analysis. Methods This is a single-centre, prospective, cohort study. According to the study criteria, 210 patients aged 60 years or older who underwent elective thoracic surgery in the Department of Thoracic Surgery at the Affiliated Hospital of Xuzhou Medical University from July to December 2022. The Pittsburgh Sleep Quality Index (PSQI) was used to divide the patients into a normal sleep group (Group H, PSQI ≤ 5) and a sleep disorder group (Group L, PSQI 5), with 105 patients in each group. Each group was managed with Conventional uniformity anaesthesia and postoperatively with an intravenous analgesic pump. General information was recorded, as well as the duration of surgery, intraoperative intravenous anaesthetic dosage, incidence of intraoperative hypotension and hypoxaemia, visual pain score (VAS) and quality of recovery (QoR-15) at different postoperative times, total number of postoperative analgesic pump compressions, length of postoperative hospital stay, and number of readmissions within 30 days after surgery. Independent risk factors for the occurrence of POD were analysed using multifactorial logistic regression. Results A total of 31 cases (30.1%) in both groups developed POD postoperatively. the incidence of POD was higher in the L group than in the H group. The difference was not statistically significant, but the duration was significantly longer (P 0.05); the VAS scores 15-30 minutes after extubation and 24 hours after surgery were significantly higher in group L than in group H (P 0.05); the total QoR-15 score at 24 hours after surgery was significantly lower in group L than in group H (P 0.05). Conclusion Preoperative sleep disturbances increase the incidence of POD in elderly thoracic patients, negatively impacting on early postoperative pain and quality of recovery, and should be taken into account by anaesthesia and clinical departments.