Objective To investigate the efect of posterolateral approach in the treatment of trimalleolar fracture and its efect on wound and fracture healing speed. Methods Atotal of 70 patients with trimalleolar fractures who were hospitalized in Hefei Orthopaedic Hospital from December 2021 to December 2022 were selected as the research objects. According to the random number table method, they were divided into control group and observation group, with 35 patients in each group. The control group was treated with traditional approach surgery, and the observation group was treated with posterolateral approach surgery. The operation related indexes, postoperative rehabilitation indexes, ankle joint function recovery and incision cosmetic satisfaction were compared between the two groups. Results The duration of operation in the observation group was shorter than that in the control group, and the intraoperative blood loss and postoperative drainage volume were lower than those in the control group (P<0.05). The wound healing time, fracture healing time and hospitalization time in the observation group were shorter than those in the control group (P<0.05). The excellent and good rate of ankle joint function in the observation group was 88.57%, which was higher than 62.86% in the control group (P<0.05). The incision cosmetic satisfaction (CS) score of the observation group was higher than that of the control group (P<0.05). Conclusion The efect of posterolateral approach in the treatment of trimalleolar fracture is good, which can efectively reduce the trauma caused by the operation, shorten the healing time and hospitalization time, improve the ankle joint function, and the patients' incision cosmetic satisfaction is high.