【Objective】To evaluate the effect of hydromorphone for postoperative analgesia on residual carbon dioxide during recovery after laparoscopic colorectal surgery.【Methods】A total of 100 patients performed with elective laparoscopic colorectal sur? gery were randomly allocated into two groups according to different patient controlled intravenous analgesia（PCIA）formula：Group H contained hydromorphone 8 mg and Group M contained morphine 40 mg. Total PCIA volume was 100 mL saline with loading volume 2 mL，background volume 2 mL/h，and lockout time was set on 15 min. Analgesia infusion pump was used in the two groups half an hour before the end of surgery. Surgery time，pneumoperitoneum time，anesthesia time，extubation time，recovery time and retention time in postanesthesia care unit（PACU）were recorded，respectively. PaCO 2 ，the pain Visual Analogue Scale（VAS）score，Ramsay sedation score，at 30 min（T0）after pneumoperitoneum，extubation time（T 1 ），30 min（T 2 ），1 h（T 3 ），2 h（T 4 ），and 24 h（T 5 ）af? ter extubation，the times of PCA compressions were recorded. Anesthesia complications during waking-up period such as postopera? tive nausea and vomiting（PONV），shoulder pain，hypersomnia，pruritus and satisfaction degree after surgery were also recorded. 【Results】Compared with group H，PaCO 2 was higher at T 2 ~ T 4 （P < 0.05）；Recovery time，extubation time and the retention time in PACU were longer after surgery（P < 0.05）；The incidence of postoperative nausea and vomiting，shoulder pain were higher in group M（P < 0.05）. Compared with group M，VAS score at T 1 ~ T 3 ，and Ramsay sedation score T 1 ~ T 4 were decreased in group H（P < 0.05）.【Conclusion】Compared with morphine，hydromorphone can increase fewer residual carbon dioxide during recovery and fewer side effects for the patients caused by that after laparoscopic colorectal surgery. Hydromorphone was a safer and more effective analgesic for postoperative analgesia than morphine.