If the electric field intensity in the detection area of the capillary cell is non-uniform, a slight change in the detection position will result in a large change in the electric field intensity, which in turn will reduce the accuracy of the zeta potential measurement results. In order to improve the accuracy and repeatability of the zeta potential measurement results, an electric field simulation was carried out for capillary cells with different electrode sizes and cell structures. By analyzing the effect of electrode size and capillary cell structure on electric field intensity uniformity, the optimal capillary cell structure was obtained.