In this article diode emission system with dielectrics on the field emitter basis is simulated. The diode system is a rotationally symmetrical electron gun with a field emission cathode on a flat substrate and a flat anode parallel to the substrate. The interior of the system domain is filled with three dielectrics. The effect of the field cathode on the electrostatic potential distribution is replaced by the effect of a finite charged line that is located at the axis of the system. The potential distribution is determined over the entire area of an electron gun. Fowler–Nordheim equation is used to calculate the emission characteristics values. The effect of dielectrics on the emission characteristics is presented.