<p>Under open-circuit faults in the windings, the fault-tolerant operation modes of dual three-phase permanent-magnet synchronous motors (DTP-PMSMs) have a negative effect on the electromagnetic vibration performance. However, the underlying causes of the effect still need to be investigated. In this paper, the mechanism of the effect of multiple fault-tolerant operation modes on the vibration performance of DTP-PMSMs is revealed. First, based on the types of open-circuit faults in the windings, the armature current distribution in each phase under the healthy mode and the fault-tolerant modes is provided. Moreover, the distributions of the armature magnetomotive force (MMF) harmonic and the air-gap electromagnetic force density harmonic are compared under different modes. The effects of the fault-tolerant modes on vibration response, output performance, and torque ripple are analyzed. It is indicated that the deterioration in vibration performance is most severe under Mode I due to the additional fifth- and seventh-order armature MMF harmonics and higher amplitude of the healthy phase current than the other modes. Due to the half-load operation, both the vibration response and torque ripple under Mode II are lower than those under Mode I. Finally, vibration tests for a 24s/22p DTP-PMSM under multiple modes are conducted to validate the theoretical analysis and predicted results.</p>