Abstract: Based on the features of damaged steel plates bonded by composite patch, a three demensional mechanical modeling of elasticity was presented in this paper. The stresses and deformation of axially stretched flat double-side bonded by composite patch were investigated. The distribution of the shear stresses within the bondline and the distribution of the axial force in the steel plate and the patch were studied. The relative stiffness of the reinforced plate versus intact plate was determined. And the relative stiffness of steel plate with a elliptical cutout after versus before reinforced by bonded composite patches and versus intact plate were evaluated. The results indicate that the stiffness of the steel plate with a circular cutout reinforced by bonded composite patches increases with the increase of thickness of the composite patch, and the amount of increasing gradually mitigates. The rehabilitation efficiency can not be effectively improved depending on increasing the thinckness of the patch alone, as more than 5 layers. The present results have validated the finite element predictions and test results.