Objective:To explore the value of clinical application of the infrared ray thermal imaging (IRTI) combined with the method of "two longitudinal and five transverse lines" in locating the perforators in the transfer of free anterolateral thigh perforator flap (ALTPF) in children.Methods:From November 2018 to November 2022, 13 children (8 boys and 5 girls) aged 2 to 12 years old (6.3 years old in average) who received free ALTPF transfers were included in this study. Causes of injury were 6 by car accidents, 2 by falls, 3 by crushing injuries and 2 by burning scars. Injury sites were 2 in head, 1 in trunk, 5 in hand and 5 in ankle. The size of soft tissue defect was 2.0 cm×4.2 cm-9.0 cm×16.0 cm, and the size of ALTPF was 2.3 cm×4.5 cm-6.0 cm×20.0 cm. The remaining wound was covered with medium thick skin grafts. IRTI combined with the method of "two longitudinal and five transverse lines" was applied to preoperatively locate the pedicle and design the ALTPF. Intraoperatively, the pedicles were explored within the region of anterolateral thigh. The rate of perforrator location and sensitivity of the infrared thermography were calculated. All donor sites were directly sutured. Standard postoperative management included anti-infection, anti-coagulation, anti-convulsion and blood volume expansion with adequate warming. Regular outpatient follow-ups were conducted through various means such as home visits, telephone calls, WeChat and text messages to observe flap survival and donor site healing.Results:All 13 patients completed the 3 to 35 (11.0±1.5) months of postoperative follow-up. All 13 flaps survived well, with good colour and texture, and without obvious bloating. Only one bloated flap had a local repair at the inner ankle with a flap thinning surgery in the stage Ⅱ surgery. Then all flaps achieved satisfaction appearance in all patients. All the donor sites healed at stage I. Two patients showed significant early scar hypertrophy in the donor site, which then gradually stabilised 12 months later. All patients had good functional recovery. Before surgery, a total of 38 perforators were discovered and 40 perforators were found intraoperatively. Of the 40 perforators, 3 were not explored before operation, which were located in the proximal part of Zone Ⅰ, Zone Ⅲ and Zone Ⅳ, respectively. The sensitivity of infrared thermography was found at 92.5% in preoperative detection and location of perforators, with a positive prediction at 97.3%.Conclusion:IRTI combined with the method of "two longitudinal and five transverse lines" in locating perforators is safe and reliable in the design of ALTPFs in children. It provides an additional and reliable option for location of perforator in the design and harvesting of ALTPFs in children.