This　paper　focuses　on　the　analysis　on　a　new　kind　of　nonlinear　resonant　motion　with　the　low-frequency　large-amplitude,　which　can　be　induced　by　the　high-frequency　small-amplitude　mode　through　the　mechanism　of　modulation　of　amplitude　and　phase.　The　system　investigated　is　a　simply　supported　symmetric　cross-ply　composite　laminated　rectangular　thin　plate　subjected　to　parametric　excitations.　Experimental　research　has　been　carried　out　for　the　first　time.　The　test　plate　was　excited　near　the　first　natural　frequency　with　parametric　forces　and　the　above　mentioned　high-to-low　frequency　mode　has　been　observed,　whose　frequency　is　extremely　lower　than　the　first　natural　frequency.　Theoretical　job　goes　to　analysis　the　above　phenomenon　accordingly.　Based　on　the　Reddy＇s　third-order　shear　deformation　plate　theory　and　the　von　Karman　type　equation,　the　nonlinear　governing　equations　of　the　simply　supported　symmetric　cross-ply　composite　laminated　rectangular　thin　plate　subjected　to　parametric　excitations　are　formulated.　The　Galerkin　method　is　utilized　to　discretize　the　governing　partial　differential　equations　into　a　two-degree-of-freedom　nonlinear　system.　Numerical　simulation　is　conducted　to　investigate　this　non-autonomous　system　subsequently.　The　results　of　numerical　simulation　demonstrate　that　there　is　a　qualitative　agreement　between　the　experimental　observation　and　the　theoretical　result.　Besides,　the　multi-pulse　chaotic　motions　are　also　reported　in　numerical　simulations.　Copyright　©　2010　by　ASME.