Abstract: The motion equations of a rotating electrorheological (ER) sandwich beam subjected to base excitation are derived. The vibration stability of the ER sandwich beam under constant angular velocity and harmonic base excitation is studied. The multiple scale method is used to determine the first order approximate analytic solutions and the necessary conditions for the existence of parametric unstable of the beam. The time responses and phase domains of the rotating ER sandwich beam for various excited parameters, electric fields, and rotating speed are presented to demonstrate the parametric dynamic stability of the beam under rotation and based joint excitation. Numerical results show that the critical value of excitation parameter of the rotating ER sandwich beam under base excitation can be adjusted when it subjected to an electric field, and the ER material layer can be used to improve the dynamic stability of the beam.