The mathematical model of electromagnetic repulsion operating mechanism of fast vacuum transfer switch (FVTS) for 400 V/630 A/12.5 kA dual power supply system is proposed, and two-dimensional rotational symmetry model of electromagnetic field simulation is established in this paper. Taking the repulsion peak value, velocity characteristics and starting time as the design goals, through analysis and comparation of the dynamic characteristics of the double coil and the metal disc repulsion mechanism, the design scheme of the operating mechanism for the FVTS with short stroke and short opening time is realized. Based on the comparative study of simulation and experiment of vacuum transfer switch prototype with fast repulsion mechanism, the 5.5 mm stroke can be completed within 5ms under the operating condition of 320 V capacitor voltage and 8000 μF, which meets the engineering application requirements of fast switching for the sensitive load.