Beam structures are prevalent in various engineering applications, such as building bridges and aircraft wall panels. Due to their low stiffness and low damping characteristics, these structures are prone to low-frequency large vibrations, resulting in structural fatigue or damage. To solve the problems of fixed structural parameters and poor adaptability of traditional sandwich beams, this study proposes a magnetically controlled intelligent sandwich beam structure based on magnetorheological elastomers. This structure can adaptively adjust its stiffness and damping according to changes in external excitation under the influence of a magnetic field, effectively suppressing vibrations. Firstly, to overcome the challenges of difficult magnetic field application and significant magnetic field attenuation in the air for traditional sandwich beams, a magnetron sandwich beam structure driven by a built-in multistage coil is proposed. Secondly, the vibration damping mechanism of the device is analyzed based on the material properties of magnetorheological elastomers. Then, the magnetic field simulation of the magnetron sandwich beam using COMSOL shows that the first-order natural frequency of the sandwich beam changes from 6.22 Hz to 9.16 Hz under a 3 A current, and the damping ratio increases by 64.4%, verifying the variable stiffness and damping characteristics of the magnetorheological elastomer sandwich beam. Finally, the broadband vibration isolation performance of the magnetron sandwich beam driven by a multistage coil is verified through multiple frequency excitation experiments.