Objective To compare the effect of patient-controlled intravenous analgesia on postoperative pain with different doses of butorphanol after cesarean section. Methods Three hundred ASA Ⅰ or Ⅱ patients underwent cesarean section were randomized to one of six groups(n=50): tramadol 200 µg·kg-1·h-1(group T), butorphanol 3.0 µg·kg-1·h-1 (group B1), butorphanol 3.5 µg·kg-1·h-1 (group B2), butorphanol 4.0 µg·kg-1·h-1 (group B3), butorphanol 4.5 µg·kg-1·h-1 (group B4), butorphanol 5.0 µg·kg-1·h-1 (group B5). Injected loading doses tramadol 50 mg in group T, butorphanol 0.5 mg in group B1－B5 after maternal separation and started the different analgesia pumps. Rest pain, motion pain and uterus systole pain VAS scores before anesthesia, in pump-opening, 30 min, 2, 4, 24, 48 h, observer’s assessment of alertnesstion/sedation(OAA/S) scores within different times or the bolus within postoperative 48 h were performed. The time to flatus, time to breastfeeding, time to lactation, side effects and satisfaction scores were recorded as well. Results Compared with group T, VAS scores of rest pain, motion pain and uterus systole pain at postoperative 24 h in group B1 were higher(P＜0.05), while no significant differences were found between group B2－B5(P＞0.05). No differences were found on the pain scores at postoperative 48 h between six groups(P＞0.05). Compare with group T, patients in group B1 need more patient controlled analgesia (PCA) bolus during postoperative 24 and 48 h(P＜0.05). Patients in group B2, B3 were with the highest satisfaction scores among all groups(P＜0.05). No significant differences were found on the time to flatus, time to breastfeeding and time to lactation, as well as OAA/S scores at different time points between six groups(P＞0.05). Conclusions PCA with butorphanol in a dosage of 3.5 µg·kg-1·h-1 or 4.0 µg·kg-1·h-1 may provide optimal postoperative analgesia after cesarean section.