The rigid-flexible coupling dynamics of a rectangular functionally graded thick plate undergoing large overall motion was investigated. Based on the first order shear deformation theory, both the transverse shear deformation and the quadratic coupling deformation were taken into account. The rigid-flexible coupling dynamic equations of the functionally graded plate were deduced by Lagrange equations. The finite element method was used to discretize the deformation field with a rectangular element having 20 degrees of freedom based on the classical thin plate theory. The dynamic simulations of the cantilever plate with different rotating speeds were carried out. The influences of function gradient index on the transverse deformation, velocity response frequency and natural frequency of the functionally graded thick plate were also discussed. The results showed that the impact of the shear deformation on structural dynamics becomes notable with an increase in the rotating speed, and the structure is more flexible as the shear deformation is taken into account.