Background Postoperative delirium is a common complication following various operative procedures with an incidence rate of 10-77 %. Methods To analyze various risk factors for postoperative delirium after spine surgery in the middle- and old-aged patients. Methods This study retrospectively reviewed 451 patients (226 males and 225 females, an average age of 65.1 +/- 18.3 years) who underwent spinal surgery in our hospital between January 2010 and August 2015. Patients who had features of acute onset and fluctuating course and any two of the other features were diagnosed with delirium. Cognitive tests consisting of Clinical Dementia Rating and Global Deterioration Scale were performed to evaluate delirium. T tests were used for statistical analysis of the difference between the two groups, and logistic regression analyses were used for determining the risk factors. Results A total of 42 (9.3 %) patients were diagnosed with delirium. Delirious and non-delirious patients had no difference in age, gender, BMI, education level, drug treatment, comorbid disease history, surgical history, preoperative blood pressure, intraoperative blood loss, blood transfusion, use of surgical implants, surgical site, use of fentanyl and propofol, and preoperative VAS score. Intraoperative hypotension and use of dezocine were related to postoperative delirium (P = 0.03 and P = 0.07). The multiple regression equation was Y = -0.11 + 0.52 x X-0 + 0.21 x X-1, where X-0 = amount of dezocine, X-1 = instances of intraoperative hypotension. Conclusion Postoperative delirium commonly occurs after spine surgery. Intraoperative hypotension < 80 mmHg and intraoperative use of dezocine represent valuable new predictors of the risk of delirium.