Abstract: The nonlinear static bending of moderate thickness rectangular plate with four free edges on a nonlinear elastic foundation is researched. Based on the Reissner theory on the moderate thickness rectangular plate, the nonlinear static control differential equations are derived for the moderate thickness rectangular plate with four free edges on a nonlinear elastic foundation, the trial functions which satisfied all of the boundary conditions are constructed and the differential equation is solved by Galerkin method, and the effects of the parametric variation of the plate and foundation to the nonlinear static bending of the thick Rectangular Plate with four free edges are discussed.