According to the elasticity energy principle, the strength model of parallel strand lumber was built. Then macroscopic elastic constant of PSL(parallel strand lumber)can be calculated on the basis of this model and theory of laminated plate. The veneer strip with affixed strain gauge were tested to got the elastic constant of veneer which was the basic data for the model. To test and verify the prediction, the experiment of different matting angle and different assembly construct has been carried out. It was seen that the mechanical model of PSL was established by the laminated plate theory could achieve a high precision of the prediction range.