Improved measurement method for the flexoelectric coefficients of nematic liquid crystal based on the renormalized transmission ellipsometry is demonstrated. For eliminating the inaccuracy in the measurement of retardation caused by multiple-beam interference in anisotropic multilayer-structured thin films, symmetrically oblique incidence transmission Ellipsometry (SOITE) has proposed and applied to the determination of the device parameters such as the cell gap, surface anchoring energy, reduced dielectric anisotropy and reduced elastic constant. We applied the SOITE technique to determine the flexoelectric coefficients (e(11) + e(33)) for the splay and bend distortion.