Abstract: A three-dimensional bending analysis was presented for an orthotropic functionally graded plate. Assuming that material properties have the same variations along the plate-thickness direction，Peano-Baker series solution was obtained for the elastic fields of the simply supported functionally graded plate under the mechanical loads on its upper and lower surfaces by means of the state space method. The correctness of the obtained series solution was validated through numerical examples. The different graded parameters toward the influence of the structural response of the plate were also studied when the material properties were of cosine function dependence on the thickness-coordinate. The numerical results show that the series solution has good convergence.