Abstract: The electrohydrodynamic equation of bubble deformation in liquid was derived based on the ellipsoid model of bubble breakdown in liquid. With the software Comsol being used to track the bubble deformation, the impact of air bubble deformation in dielectric liquid under strong electric field was discussed. The results show that the spherical bubbles turn into elliptical ones with the combined action of electric stress and surface tension. In order to avoid bubble breakdown, applying pressure is a practical measure. Moreover, the applied pressure and the bubble aspect ratio are in direct proportion to electric field strength and original bubble radius.