In this paper, the carbon fiber mechanical properties of wood composite board were discussed. The microscopic structure of the composite material was analyzed based on finite element method. A unit cell model was established, and element stiffness matrix of the model was developed. The model was used to predict the mechanical properties with feasible and accurate affects. The results of experiment showed that after carbon fiber being mixed, the MOE, the MOR and the IB of medium density fiberboard was significantly improved.