Nonlinear　dynamics　of　a　sandwich　plate　with　viscoelastic　soft　core　in　supersonic　flow　are　investigated　by　considering　the　in-plane　periodic　loading.　Using　Reddy＇s　third-order　shear　deformation　theory　and　von　Karman＇s　nonlinearity,　the　governing　partial　differential　equations　are　derived　by　Hamilton＇s　principle　and　then　truncated　into　a　set　of　ordinary　differential　equations　by　Galerkin　method.　The　critical　speed　for　flutter　is　discussed　by　employing　the　linear　theory.　Further,　the　method　of　multiple　scales　is　used　in　the　nonlinear　dynamical　analysis　of　the　truncated　system.　The　Poincare　map　is　numerically　calculated　to　identify　dynamical　behaviors.　The　bifurcation　diagrams　are　presented　for　varying　the　dimensionless　in-plane　loading　fluctuation　amplitude　and　the　Mach　number　related　dimensionless　parameter　while　other　parameters　are　unchanged.