Objective:To observe and summarise the clinical effect of free groin flap in repairing of soft tissue defects in extremities, and to explore the selection of main vessel in a flap.Methods:From January 2018 to January 2021, 146 patients with soft tissue defects in extremities were treated with free groin flaps in the Department of Hand and Microsurgery, Guangxi Guilin Xing'an Jieshou Orthopaedic Hospital. There were 126 patients with traumatic wound and 20 with chronic ulcer. In addition, 86 of the patients with bone fracture and exposure of internal fixator, 18 with tendon, nerve or artery injuries or defects. There were 6 patients with severe infection and other 3 with deep dead space. The sizes of wound ranged from 2.0 cm×3.0 cm to 25.0 cm×6.0 cm. The flap was the same size as the wound and not enlarged. Firstly, the superficial branch of superficial iliac circumflex artery was explored as the axial artery for all the flaps, then the blood supply vessels of the flap were selected according to the availability of the axial artery. The size, course, adjacent and possible length to be freed of the axial artery and the accompanying veins of a flap were recorded. The donor sites were directly sutured and closed. All patients were included in the postoperative follow-up at outpatient clinic.Results:Free groin flap were used to repair the wounds in all patients. However, the main blood supply vessel of the flap was not constant, and it was often required to adjust the way of flap harvesting. Superficial circumflex iliac artery was taken as the axial vessels in 141 patients (96.6%), among them, 133 cases(94.3%) had the superficial branch as the axis and 5 cases (3.6%) had deep branch as the axis. Three patients (2.1%) had the bone and soft tissue defects reconstructed with vascularised iliac mosaic osteocutaneous flap with superficial circumflex iliac artery as axial vessel and 5 cases(3.4%) had the superficial epigastric artery as axial vessel. The axial arteries were measured as follow: the superficial branch of the superficial circumflex iliac artery was 0.5-0.9 mm in diameter and 7.0-9.0 cm in length, the outer diameter of the deep branch was 1.2-1.4 mm and 9.0-11.0 cm in length, and the outer diameter of superficial epigastric artery was 1.0-1.6 mm and 8.0-11.3 cm in length. All the flaps survived smoothly after surgery and the follow-up period ranged 6-40 (mean 26) months. The texture of the flaps was soft with good function.Conclusion:Free groin flap can be used to repair soft tissue defects in extremities. The main axial vessel is the superficial branch of the superficial circumflex iliac artery, followed by the deep branch or the trunk. The superficial abdominal artery can also be used as an axial vessel. Under the circumstances, the flap design needs to be adjusted without changing the supply area