Abstract：A nonlinear dynamical equation of the small deformation thin rectangular plates on nonlinear elastic foundation subjected to harmonic excitation is established. It is transferred to be a nonlinear vibration equation by Galerkin¢s method. By means of the method of the multiple scales the first approximate solution of the primary resonance of the system is acquired，and numerical calculation is carried out. The transition variety and bifurcation diagram of the unfolding parametric plane are given. The response curves of the primary resonance are affected by damping parameter，foundation parameter and geometry parameter. It is pointed out that with the increasing of foundation coefficient and damping coefficient，the amplitude reduces. With the increasing of the thickness of thin plate，the amplitude increases.
