Abstract: Polarity switching control (PSC) effectively suppressed the synchronous unbalance vibration of the active magnetic bearing(AMB) supporting rigid rotor system in high speed motor before and after the cylindrical mode, and the impact of switching polarity on the system was reduced by disturbance observer. However, considering the conical mode, the PSC could not guarantee the synchronous unbalance vibration suppression in the full rotational speed range including the cylindrical mode and conical mode frequencies, and the system stability also changed. In order to suppress the synchronous unbalance vibration of the AMB rigid rotor system in the full rotational speed range, this paper proposed a synchronous unbalance vibration suppression method based on 4-factor polarity switching control (4-FPSC), which switched polarity twice and adjusted four polarity factors to suppress synchronous vibration before and after these two rigid mode modes. Besides, the 4-FPSC did not make an impact on the system, and the design of the disturbance observer was also avoided. Finally, simulation and experiment results verified the method based on the 4-FPSC can effectively suppress the synchronous unbalance vibration of AMB rigid rotor system in the full rotational speed range with two rigid modes.