Objective:To evaluate the efficacy of ultrasound-guided modified brachial plexus block at costoclavicular space (CCS) for forearm surgery.Methods:Eighty patients of both sexes, aged 18-75 yr, with body mass index of 18-30 kg/m 2, of American Society of Anesthesiologists physical status Ⅰ or Ⅱ, scheduled for elective forearm surgery from September 2020 to May 2021 in our hospital, were randomized into 2 groups ( n=40 each) using a random number table method: single-injection control group (group C) and double-injection modified group (group T). Single-injection was performed in the anterior chamber of CCS in group C, double-injection was performed in the anterior and posterior chambers of CCS in group T, and the solution injected in both groups was a mixture (20 ml) of 1.0% lidocaine and 0.375% ropivacaine.The effect of block, onset time of block, completion time of block and duration of block for each nerve branch and anesthesia-related adverse reactions were recorded at 5, 10, 15, 20, 25 and 30 min after injection of local anesthesia. Results:Compared with group C, the rate of motor block of radial nerve at 5-20 min after injection of local anesthesia, the rate of sensory block of musculocutaneous nerve and radial nerve at 10 and 15 min after injection of local anesthesia, the rate of motor block of median nerve at 15-30 min after injection of local anesthesia and the rate of sensory and motor block of ulnar nerve at 20-30 min after injection of local anesthesia were significantly increased, and the onset time and completion time of block were shortened in group T ( P<0.05). There was no significant difference between the two groups in the duration of block and anesthesia-related adverse reactions ( P>0.05). Conclusions:Ultrasound-guided modified brachial plexus block at CCS provides better efficacy for forearm surgery.