In this paper the calculation of the electrostatic potential distribution for a two-dimensional diode emission system with a blade-shaped field emitter on a plane substrate is presented. The anode is a plane parallel to the substrate. To calculate the potential distribution, the effect of the emitter is simulated as the effect of a charged line, so that the emitter surface is zero equipotential. To solve the boundary problem, the method of separation of variables in Cartesian coordinates is used. All geometrical sizes of the diode system are parameters of the problem.