The surface-conduction electron-emitter display(SED) based on tunneling effect is a newly developed flat panel display. It has obvious technical advantages and excellent characteristics and is praised as one of the most advanced displays. Based on the theory of electromagnetism, an equivalent physical model of a single pixel of SED is established. In particular, it shows the exterior charge densities in different parts of the pixel. Furthermore, the electric potential and electric field intensity are studied in detail, and their distribution is simulated with the help of MATLAB 6.5 Software. Finally, a theoretical analysis of the simulated curved surface is given, and the electrical behavior as well as the emission mechanism is explained comprehensively. In order to further interpret the behavior of electrons in SED, we compare this model with the multi-scattering model and the inertial centrifugal force model respectively. It is found that within the limits of error our conclusion on electric field distribution is consistent with that of the inertial centrifugal force model.