The development of low-frequency-driven liquid crystal displays (LCDs) has recently received intense attention to open up low-power consumption display devices, such as portable displays, advertising panels and price tags. In fringe-field switching (FFS) LCD mode, a unidirectional electric field gives rise to head-tail symmetry breaking in liquid crystals, so that the flexoelectric effect, a coupling between the elastic distortion and the electric polarization, becomes enormously significant. The effect is thus linked to an unusual optical effect, which badly damages the quality of images by image-flickering, and this image-flickering is mainly caused by transmittance difference between the applied signal frames. Here, we intensively investigate the mechanism of the transmittance deviation, and propose an essential and promising approach to solve the poor image-quality, that is, symmetrization of electric fields between the frames. The result of our work clearly demonstrates that the field-symmetry is crucial to reduce the image-flickering, and it can be obtained by optimization of the thickness of an insulation layer with respect to the ratio of the space between electrodes to the electrode width.