Objective To study the stress distributions of mandible defect by reconstruction with polyetheretherketone (PEEK) and its composite reconstruction plate through three-dimensional finite element analysis. Methods The finite element models of reconstruction plate of titanium alloy, PEEK, carbon-fiber-reinforced polyetheretherketone (CFR)-PEEK with 30% endless carbon fibers and CFR-PEEK with 68% endless carbon fibers were established by CBCT scanning，Mimics software，SolidWorks, Geomagic Studio and ANSYS Workbench software, and titanium alloy served as control. Two occlusal situations were simulated in the mandible model. Loading I: anterior region loading with 300 N; loading II: left posterior region with 300 N. Results The ratio of the maximum Von Mises stress of the reconstructed plate to its yield strength under two load situations: PEEK system ＞ 30%CFR-PEEK system ＞ titanium alloy system ＞ 68% CFR-PEEK system; the maximum stress of the mandible: PEEK system ＞ 30% CFR-PEEK system ＞ titanium alloy system ＞ 68% CFR-PEEK system. In the PEEK system, the maximum Von Mises stress of reconstructed plate and mandibular exceeded its yield strength under loading I; in the other systems, the maximum Von Mises stresses of mandible and reconstruction plate were below the yield strength. Conclusions The reconstruction plate of CFR-PEEK with 68% endless carbon fibers distributed the stresses in a similar manner as the titanium reconstruction plate, which could meet the mechanical strength requirements of mandible defect reconstruction. The fracture risk of the reconstructed plate was lower than that of titanium alloy, but the incidence of stress shielding was slightly higher. The result can provide references for the selection of materials and clinical application of reconstruction plate for mandibular defects.