Abstract: The nonlinear dynamic responses and the dynamic stress of a circular plate in thermal environment were studied. The effect of geometric nonlinearity and temperature-dependent material properties were both taken into account. The material properties of the functionally graded plate were assumed to vary continuously through the thickness according to a power law distribution of the volume fraction of the constituents. Using the principle of virtual work, the nonlinear partial differential equations of functionally graded plate subjected to transverse harmonic excitation and thermal loads were derived. For the circular plate with clamped immovable edge, the Duffing nonlinear forced vibration equation was deduced by using Galerkin method. Through the numerical example given in the paper, the bifurcation diagram for material's volume fraction index, phasepotrait, Poincare map and the dynamic stress variation were plotted. Besides, the influences of materials volume fraction index and thermal loads on the nonlinear dynamic response of functionally graded plate were discussed. The results show that periodic, multiplier periodic and chaotic motions exist for the functionally graded plate with the change of the volume fraction index. The dynamic stress at the center of the circular plate varies sharply when the system appears bifurcation or chaos and becomes unpredictable when the system appears chaotic motions.