An　analysis　on　nonlinear　dynamic　characteristics　of　a　simply　supported　functionally　graded　materials　(FGMs)　rectangular　plate　subjected　to　the　transversal　and　in-plane　excitations　is　presented　in　the　time　dependent　thermal　environment.　Here　we　look　the　FGM　Plates　as　isotropic　materials　which　is　assumed　to　be　temperature　dependent　and　graded　in　the　thickness　direction　according　to　the　power-law　distribution　in　terms　of　volume　fractions　of　the　constituents.　The　geometrical　nonlinearity　using　Von　Karman＇s　assumption　is　introduced.　The　formulation　also　includes　in-plane　and　rotary　inertia　effects.　In　the　framework　of　Reddy＇s　third-order　shear　deformation　plate　theory,　the　governing　equations　of　motion　for　the　FGM　plate　are　derived　by　the　Hamilton＇s　principle.　Then　the　equations　of　motion　with　two-degree-of-freedom　under　combined　the　time-dependent　thermomechanical　loads　can　be　obtained　by　using　Galerkin＇s　method.　Using　numerical　method,　the　control　equations　are　analyzed　to　obtain　the　response　curves.　Under　certain　conditions　the　periodic　and　chaotic　motions　of　the　FGM　plate　are　found.　It　is　found　that　because　of　the　existence　of　the　temperature　which　relate　to　the　time　the　motions　of　the　FGM　plate　show　the　great　difference.　A　period　motion　can　be　changed　into　the　chaotic　motions　which　are　affected　by　the　time　dependent　temperature.