Based upon the anisotropy of electric polarization,the nonolinear oscillation equation of the ellipsoid in electric field is constructed by considering the rotative moment between electric field and the induced dipole moment on metallic ellipsoid of field intensity gauge. The oscillation period relative to the amplitude and electric intensity is calculated.An expression of exact computation to measure the electric field intensity is achieved.The impact of the amplitude parameter upon the experiment calculation is analyzed and the method to determine the amplitude is contributed.A contrast to the computed resuls by means of linear oscillation is undertaken to show the raising effect to the calculation precision by considering nonlinearity in oscillation.