Objective To observed the effect of dexmedetomidine as an adjunction with ropivacaine in supraclavicularbrachial plexus block. Methods 55 subjects with elective upper extremity operation were randomly divided into two groups: DEX group and control group. The drugs in DEX group was 30 μg dexmedetomidine (0.3 mL) + 0.5% ropivacaine, 20 mL in total. And the one in control group was normal saline (0.3 mL) +0.5% ropivacaine, 20 mL in total. After the operation of brachial plexus block, the value of sensory and motor block of brachial plexus and the onset time were evaluated and recorded according to the protocol. Vital signs and adverse events were monitored and recorded regularly during the operation.Postoperative vital signs, postoperative analgesia time, duration of brachial plexus sensationsensory and motion block, postoperative nausea and vomiting score, dosage of remedial analgesics and adverse events were assessed and recorded in 24 hours after surgery. Results In terms of sensory and motor onset time of brachial plexus, duration of sensory and motor block and postoperative analgesia, DEX group was longer than the control group, with statistical differences (P<0.05).There were no significant statistical differences between the two groups in postoperative vital signs, the amount of remedial analgesic drugs, postoperative nausea and vomiting scores, adverse events etc(P>0.05). Conclusion As an adjuvant, dexmedetomidine (30 μg) can accelerate the onset time of ropivacaine in the supraclavicular approach of brachial plexus block.It can also increase the postoperative analgesia time and sensory and motor block time of brachial plexus.With less impact on the vital signs of patients, the efficacy and clinical safety of dexmedetomidinecan be found in our study.