Objective To explore the effect of ropivacaine at different temperatures on skin temperature and blockage characteristics after supraclavicular brachial plexus block using infrared thermography. Methods A total of 63 patients who were scheduled for open reduction internal fixation due to metacarpal fractures, men or women, age≥18 years old, and American Society of Anesthesiologists (ASA) grades Ⅰ−Ⅲ, were selected. According to the random number table method, they were divided into three groups (n=21): a warmed group (injection with 15 ml of 0.5% ropivacaine at 37 °C, group W), a normothermic group (injection with 15 ml of 0.5% ropivacaine at 23 °C, group N) and a hypothermic group (injection with 15 ml of 0.5% ropivacaine at 4 °C, group L). All the patients performed supraclavicular brachial plexus nerve block under ultrasound guidance. Primary outcomes: skin temperature changes in the area beneath the thumb nail bed (0.81 cm2) and the area beneath the little finger nail bed (0.81 cm2) 5−30 min after block observed using infrared thermography. Secondary outcomes: the onset of sensory blockade in the surgical area, the duration of postoperative analgesia maintenance in the surgical area, the consumption of hydromorphone within postoperative 24 h and the incidence of adverse events after blockade. Results After nerve blockade for 5-30 min, group W showed higher skin temperature innervated by the radial and ulnar nerves than group N and group L (all P<0.05), while group N had higher skin temperature innervated by the radial and ulnarnerves than group L (all P<0.05). After nerve blockade for 30 min, the skin temperature innervated by the radial nerve in group W was higher than that by the ulnar nerve (P<0.05). There was no statistical difference between skin temperature innervated by the radial and ulnar nerves in group N (P>0.05). The skin temperature innervated by the radial nerve in group L was lower than that by the ulnar nerve (P<0.05). The onset time of sensory blockade in group W were shorter than that in group N and group L (all P<0.05), while the group L required longer onset time than group N (P<0.05). The duration of analgesia maintenance in group W were longer than that in group N and group L (all P<0.05), and there was no statistical difference as to the duration of analgesia maintenance between group L and group N (P>0.05). The consumption of hydromorphone within postoperative 24 h in group W were lower than that in group N and group L (all P<0.05), while the group L consumed higher amounts of hydromorphone within postoperative 24 h than group N (P<0.05). There was 1 case of injection pain during local anesthetic injection in group L, while no adverse events were observed in the other two groups. Conclusions After brachial plexus nerve block by ropivacaine at 37 ℃, the skin temperature innervated by the radial and ulnar nerves increase by 23 ℃ and 4 ℃, respectively, through infrared thermography. Compared with ropivacaine at 23 ℃ and 4 ℃, ropivacaine at 37 °C can shorten the onset time of sensory blockade, prolong the duration of postoperative analgesia maintenance, and reduce oxycodone consumption within 24 h after surgery.