In this article, the state of stress in tensile-shear Strength-testing Pieces of plywood wasanalyzed with the theory of Single—lap joint. The results showed that there are three kinds of stresses in the testing pieces, the tensile stress in the face veneer and the shear stress in the coreveneer, both of which are parallel to the load P, and the peeling stress in the adhesion surface, which is perpendicular, to the load P. These stresses distribute unevenly and the maxmium values all appear at the corner of kerfs. the stress concentration coefficients are mainly affected by the thickness ratio among the thickness structure factors and the effect of the face veneers, thickness on the stress concentration coefficients may be ignored in practice.Three kinds of 3-ply panels were made of Ash, Basswood and Lauan in the laboratory. The results of the tensile—shear strength test showed that the thickness ratio has, considerable influence on the tensile—shear strength. The reation between them could described with a quadratic equation which varied with species of veneers and from which the thickness coefficient equation and the thickness coefficients were made. The thickness coefficient must be of consideration with the consisting species of plywood:.