This study developed a zygomaticomaxillary complex (ZMC) patient-specific repairing thin (PSRT) implant based on the buttress theory by integrating topology optimization and finite element (FE) analysis. An intact facial skeletal (IFS) model was constructed to perform topology optimization to obtain a hollow skeleton (HS) model with the structure and volume optimized. The PSRT implant was designed based on the HS contour which represented similar trends as vertical buttress pillars. A biomechanical analysis was performed on a ZMC fracture fixation with the PSRT implant and two traditional mini-plates under uniform axial loads applied on posterior teeth with 250 N. Results indicated that the variation in maximum bone stress and model volume between the IFS and HS models was 15.4% and 75.1%, respectively. Small stress variations between the IFS model and repairing with a PSRT implant (2.75-26.78%) were found for compressive stress at frontal process and tensile stress at the zygomatic process. Comparatively, large stress variations (30.67-96.26%) with different distributions between the IFS model and mini-plate models were found at the corresponding areas. This study concluded that the main structure/contour design of the ZMC repair implant according to the buttress position and orientation can obtain a favorable mechanical behavior.