[Objective] To compare the clinical outcomes of hollow screw fixation and buttress plate fixation of posterior malleolar fracture in trimalleolar ankle fractures. [Methods] The clinical data of 68 patients who underwent open reduction and internal fixation for posterior malleolar fragment from February 2018 to February 2021 were analyzed retrospectively. 41 cases were fixed with hollow screws (screw group), while 27 cases fixed with buttress plate (plate group). The perioperative data, follow-up function scores and radiographic documentations were compared between groups. [Results] All the patients performed the surgical procedures successfully. There was no significant difference in perioperative parameters (operation time, incision length, intraoperative bleeding, days in hospital, incision infection, vascular embolism events, implant malposition, and post-traumatic arthritis) between the two groups (P>0.05). The incidence of toe flexion contracture and implant irritation in the buttress plate group was higher than screws group with significant difference (P<0.05). All patients were followed up for 12 to 48 months, with a mean of (23.44 ± 11.59) months. There was no significant difference in AOFAS, VAS and the difference of range of motion between the two groups in 3-month and the latest follow-up (P>0.05). Bone union time of the screw group was shorter than plate group with significant difference (P<0.05),whereas medial clear space (MCS), tibiofibular clear space (TFCS) and Step-off/ Gap distance were no significant difference between two groups (P>0.05). [Conclusion] Both hollow screws and buttress plate provide adequate fixation for the posterior ankle fracture fragments with satisfactory functional outcomes, however, it is indispensable for progress of post-traumatic arthritis. Compared with the buttress plate fixation, the hollow screws fixation is simpler and more effective with less implant related complications.