In this paper, the non-linear ultraharmonic resonance of a conductive beam plate in a magnetic field subjected to some mechanical loadings is studied. Base on nonlinear electro-magneto-elastic equations of the plate and the expression of electromagnetic forces, the vibration equations of thin beam plate under uniform transverse magnetic field and mechanical loadings are obtained. By use of the Galerkin’s method, the differential equation of the nonlinear vibration is derived consequently. By mean of multiscale method, the amplitude and frequency resonance equations in steady state are arrived at. By some examples, the amplitude-frequency curves, time history curves are derived. The influences of plate thickness, magnetic field and excitation amplitude on vibration properties of system are analyzed.