Objective: To explore the efficacy of dexmedetomidine in ultrasound-guided brachial plexus block (BPB) and its influences on limb ischemia-reperfusion injury. Methods: A total of 106 patients who underwent internal fixation for radius and ulna racture and ultrasound-guided BPB anesthesia in the hospital from August 2017 to August 2020 were enrolled. They were randomly divided into an observation group and a control group, 53 cases in each group. The control group was given ropivacaine, while the observation group was given dexmedetomidine hydrochloride on the basis of the control group. We compared changes of the two groups in each index at 5 min before block (T0), 10 min after block (T1), 15 min after block (T2), 30 min after block (T3), 60 min after block (T4) and 90 min after block (T5), immediately after surgery (T6), at 4 h after surgery (T7), 8 h after surgery (T8), 24 h after surgery (T9) and 48 h after surgery (T10) and the onset and maintenance time of sensory and motor nerve block in them. Besides, we also compared other changes between the two groups, including heart rate (HR) and mean arterial pressure (MAP) at T0, T1, T2, T3, T4 and T5, serum malondialdehyde (MDA) and superoxide dismutase (SOD) at T0, T6, T7, T8, T9, and T10, tumor necrosis factor α (TNF-α) and interleukin 8 (IL-8) at T0, T6, T7, T8, T9 and T10, scores of VAS pain and Ramsay sedation at T7, T8, T9 and T10, as well as the incidence of adverse reactions. Results: The onset time of sensory and motor nerve block in observation group was shorter than that in the control group, while its maintenance time was longer than that in the control group, and the differences were statistically significant (P<0.05). At T1, T2, T3, T4 and T5, the HR and MAP in the observation group were lower than those in the control group, and the differences were statistically significant (all P<0.05). At T7, T8, T9 and T10, level of serum SOD in observation group was higher than that in the control group, the MDA lower than that in the control group, the levels of IL-8 and TNF-α lower than those in the control group, and the differences were statistically significant (all P<0.05). At T7, T8 and T9, patients’ scores of VAS pain in observation group were lower than those in the control group, while the scores of Ramsay sedation were higher than those in the control group, and the differences were statistically significant (all P<0.05). At T10, there were no statistically significant differences in scores of VAS pain and Ramsay sedation between the two groups (P>0.05). There was no statistic significance about the differences in the incidence of nausea, vomiting or sleepiness between the two groups (P>0.05). The incidence of intraoperative bradycardia in observation group was higher than that in the control group (13.21% vs 1.29%), and the differences were statistically significant (P<0.05). Conclusion: Dexmedetomidine can effectively shorten the onset time of sensory block in patients undergoing internal fixation for radius and ulna fracture under ultrasound-guided BPB anesthesia, prolong the maintainance time of sensory block, maintain hemodynamic stability, and alleviate ischemia-reperfusion injury, but it may increase the incidence of intraoperative bradycardia.