Objective To construct a three-dimensional finite element model of reconstructed mandible and analyze the stress distributions of the model. Methods CT scan and CAD/CAM software was used to develop the three-dimensional finite element model of reconstructed mandible and stress analysis was performend with ANASYS 7.0 software. Results The three-dimensional finite element models of normal mandible and reconstructed mandible were constructed. The stress analysis discovered an unbalanced stress distribution in the mandible. Conclusion Reconstructing mandible with fibular flap not only damages its structure, but also induced the badness of its biomechanical environment, in which condyle was the most sensitive region during the stresses in the mandible were changed.