Objective To investigate best timing of ultrasound-guided rectus sheath block in single-site laparoendoscopic surgery.Methods A total of 63 patients underwent elective single-site laparoendscopic surgery for benign gynecological tumors in Gynecology Ward of the Second Affiliated Hospital of Wenzhou Medical University from August 2021 to January 2022 were selected as study subjects.They were divided into Group E(32 cases)and Group O(31 cases)by using a random number table method.After excluding three cases,60 patients were finally admitted,with 30 cases in each group.Group E underwent preoperative ultrasound-guided rectus sheath block,and group O underwent postoperative ultrasound-guided rectus sheath block.Numerical rating scale(NRS)score of immediately after extubation(T1),12-hour after surgery(T2),and 24-hour after surgery(T3)in resting and active status were compared between two groups;mean arterial pressure and heart rate before and after incision were compared between two groups;intraoperative dose of remifentanil,postoperative oxycodone and rate of postoperative analgesic relief were compared between two groups;time of entry and operation were compared between two groups;and occurrence of nerve block complications in two groups was recorded.Results Overall analysis found that there were significant differences in comparison of time points and interaction of resting NRS scores in two groups(P<0.05),as well as there were significant differences in comparison of time points of active NRS scores in two groups(P<0.05).Further pairwise comparison,within-group comparison:NRS scores of rest status and active status at T2 and T3 in group O were significantly lower than those at T1(P<0.05);NRS scores for rest status at T3 was significantly lower than that at T1 in group E,and NRS scores for active status at T2 and T3 were significantly lower than those at T1 in group E(P<0.05).Comparison between groups:NRS scores for rest and active status at T1 were significantly lower in group E than that in group O(P<0.05).After skin incision,mean arterial pressure in group O was significantly higher than before skin incision,and heart rate in group O was significantly faster than before skin incision(P<0.05).No abdominal puncture,puncture site infection,local anesthetic poisoning,or other complications occurred in either group.Conclusion In single-site laparoendoscopic gynecological surgery,ultrasound-guided preoperative rectus sheath block can provide better analgesic effect for patients in the early postoperative stage,and changes in heart rate and mean arterial pressure before and after incision are smaller,which is worthy of recommendation.