Abstract: Objective:To investigated the effects of dextromethorphan on postoperative pain and patient-controlled epidural analgesia （PCEA） . Methods:40 patients scheduled for selective surgery under combined spinal and epidural anesthesia were randomly divided into two groups with 20 patients each. Dextromethorphan（20mg） were injected intramuscularly 30min before operation in group A, and the same volume of sodium chloride was injected in group B. PCEA began when patients’ pain intensity came to 2～3 on a 10-point VAS. Analgesic doses, adverse effect, pain and feeling VAS score were recorded 2h, 4h, 6h, 24h and 48h after PCEA. Results:Pain score and analgesic doses were less in group A,feeling score was higher in group A than that in group B（4～48h,P＜0.05）.Adverse effects were similar in the two groups（P＞0.05）. Conclusions:dextromethorphan IM 30min before operation can improve the effect of PCEA without increasing the adverse effects.