Ferrofluids are colloidal dispersion of magnetic nanoparticles in carrier liquid. It has been found that the use of ferrofluid as insulation oiil can improve the heat transfer and dielectric characteristics. Those should be because the fluid is affected by the dielectropphoresis force as well as magnetic force. Through the previous researches based on measuring the dielectric breakdown voltage of the fluids and visualizing the magnetic nanoparticles using microchannel, we found that the dielectric breakdown voltage of fluids is higher than that of pure transformer oil and magnetic nanoparticles move into near the electrode. In this study, we predicted the movement of magnetic nanoparticles using the results of electromagnetic field calculations and described the reason why the dielectric breakdown voltage of the fluids should be changed positively and negatively.