Objective To evaluate the efficacy and safety of postoperative analgesia in continuous Interscalene brachial plexus block by different strength ropivacaine mesylate combined with sufentanil.Methods Ninety cases of upper limb surgery in continuous peripheral nerve block (CPNB) were selected.The patients after the operation were divided randomly into three groups (A,B,and C):A group was treated with 0.158％ ropivacaine mesylate + 0.5 μg/ml sufentanil,B group with 0.238％ ropivacaine mesylate + 0.5 μg/ml sufentanil,and C group with 0.238％ ropivacaine mesylate.20 minutes before the end of surgery,controlled analgesia device was connected with infusion rate 0.05 ml/(kg · h),PCA 1 ml,and lock time 15 min.The pain visual analog score (VAS),Ramesay sedation score,and postoperative motor nerve block recovery ratings (modified Bromage classification) were recorded at the 4,8,16,32,48 h time point postoperatively.The times of using PCA and the frequency of the adverse reaction were also recorded.Results Three groups all got good analgesic effect at 4,8,16,32,48 h time point postoperatively (VAS 1.58 ± 9 ; 1.90 ± 0.8 ; 1.62 ± 0.6 ; 1.59 ± 0.7 ; 1.53 ± 0.7) (P ＞ 0.05) ; There were no significant difference among the three groups in Ramesay score,modified Bromage score,limb discomfort,nausea,vomiting,lethargy,pruritus and respiratory depression (P ＞ 0.05),but the time of using PCA in A group were significantly more than that in B or C group (P ＜ 0.05).Conclusions Sufentanil can enhance the analgesic effect significantly when the ropivacaine mesylate is in low concentrations (0.158％ ～0.238％),but when the ropivacaine mesylate concentration get up 0.238％,there will be similar analgesic efficacy and safety between ropivacaine mesylate only and ropivacaine mesylate combined with sufentanil.