Abstract: Classical plate and shell finite elements are derived from corresponding theories of plate and shell, and the theories of plate and shell are based on spatial theory of elasticity and plate-shell assumptions. In this paper, the fundamental plate and shell assumptions are directly introduced into the 20-node spatial isoparametric finite element. By modifying the elastic matrix of the spatial isoparametric finite element, one new plate element suitable for analysis of thick and thin plates and shells 20-node degenerated solid plate element, is developed. The degenerated solid plate element is used in static analysis of one open cylindrical thin shell and the natural vibration analysis of thick and thin plates. Numerical results show that the degenerated solid plate element has the advantages of good convergence, stability and higher precision. Moreover, the element can also be used to analyze the vibration of curved plates with variable thickness, laminated plates and shells.