Objective To observe and compare the analgesic effects and adverse reactions during patient-controlled epidural analgesia (PCEA) and patient-controlled intravenous analgesia (PCIA) after thoracic surgery. Methods Sixty patients scheduled for elective thoracotomy in our department from January 2015 to June 2016 were prospectively recruited in this study. They were randomly divided into PCEA group (sufentanil 30 μg+ropivacaine 300 mg+0.9% NaCl to 250 ml, single dose 2 ml, continuous infusion 5 ml/h, lock time 15 min) and PCIA group (sufentanil 200 μg +0.9%NaCl to 250 ml, single dose 2 ml, continuous infusion 5 ml/h, lock time 15 min). The analgesic effects, including resting pain and motor pain, were assessed by visual analogue scale (VAS) at 4,4 and 48 h after surgery. Meanwhile, sedation status was observed by Ramsay sedation scale, and the adverse reactions (hypotension, respiratory depression, nausea and vomiting, weak cough, restlessness and delirium) were recorded. SPSS statistics 22.0 was used to perform the statistical analysis. Analysis of variance or Chi-square test was employed for comparison between groups in different data types. Results The VAS values of resting pain and motor pain were significantly lower in the PCEA group than in the PCIA group at 4,4 and 48 h after operation (P<0.05). At 4 and 24 h, the PCEA group had better Ramsay sedation score than the PCIA group, but no such difference was found at 48 h after operation between the 2 groups. The incidence rates of hypotension, respiratory depression, nausea and vomiting, weak cough restlessness and delirium were lower in the PCEA group than in the PCIA group, but there was no statistical difference. Conclusion For postoperative analgesia after thoracic surgery, PCEA with 0.12% ropivacaine combined 30 μg sufentanil shows better analgesic effect than PCIA with 200 μg sufentanil, and may has less adverse reactions at the same time.