A trimagnet vibration isolator was proposed for the purpose of lowfrequency vibration isolation of submarine mechanical equipments. The analytical magnetic force and stiffness models were established based on the equivalent charge method and the structure parameters of the rectangular magnet were optimized. A trimagnet vibration isolator with the rectangular permanent magnets was proposed. The approximate expression of the magnetic stiffness was obtained through curve fitting. The dynamic equation of the vibration isolation system was built, the first approximation of the primary resonance was achieved with the harmonic balance method, and the effects on the force transmissibility caused by the excitation amplitude and damping ratio were discussed. A trimagnet vibration isolator test rig was designed, and experiments were carried out to evaluate the force transmissibility under excitations with different frequency, and to compare with those of the corresponding linear vibration isolator.The results show that the trimagnet vibration isolator with the characteristics of highstaticlowdynamicstiffness and smaller peaks of resonance, can provide a novel approach for the lowfrequency vibration isolation of submarine mechanical equipments.