Abstract: The electric demulsification has been widely applied in many engineering fields. In order to explore the electrodynamics mechanism of electro-demulsification for cooking oil emulsion, authors measured the dispersed droplet diameter for W/O corn oil emulsion by using Winner99 particle image analyzer. The electric agglutination and dispersion characteristics were analyzed for dispersed droplets under different voltages. A simplified theoretical model was established according to theoretical analysis and experimental data. The results from theoretical model and experimental data showed that the threshold voltage for electric dispersion was about 5 700 V. The operation voltage should be in range of 1 000-5 000 V for a better water-oil separation efficiency.