Objective To compare the efficacy of transfibular approach and posterolateral approach in the treatment of posterior external rotation of type III-IV ankle joint fractures. Methods A total of 158 patients with supination external rotation of type III-IV ankle joint fractures were selected and divided into group A and group B according to the surgical approaches. 61 cases in group A were given internal fixation via transfibular approach , and 97 cases in group B were given internal fixation via posterolateral approach. The operative time, intraoperative blood loss, hospital stay, fracture healing time and prognosis were compared between the two groups. Results There were no significant differences in the operative time and hospital stay between the two groups(P>0.05). The intraoperative blood loss in group A was lower than that in group B, and the fracture healing time in group B was shorter than that in group A(P<0.05). The ankle-hindfoot score of AOFAS in group B was higher than that in group A, and the overall prognosis was better than that in group A(P<0.05). Conclusion Posterolateral approach has better effects than transfibular approach in the treatment of supination external rotation of type III-IV ankle joint fractures.