Local decay and insect infestation are common damage types in the flexural members of ancient buildings, such as beams and columns. In the framework of continuum mechanics and damage mechanics, the elastic-plastic damage constitutive model of wood was established, and the corresponding constitutive subroutine was developed based on the user-defined material subroutine UMAT in ABAQUS. The correctness of the constitutive model was verified based on the three-point bending wood beam test in the existing literature. Through the artificial prefabrication of local square groove, the local decay and local insect infestation on the actual wood beams and columns are simulated equivalently. Based on the developed constitutive model, the corresponding finite element model was established, and the correctness of the model was verified by the existing tests of the research group. The results indicated that the elastic-plastic damage constitutive model of wood and the finite element model of timber beam and column can reflect the nonlinear stress and damage evolution behavior of damaged beam and column members.