The problem of the influence of boundary conditions on the surface of emitting bodies on particle flows in their vicinity is studied in this paper. The solution to this problem is actual and relevant both for studying the behavior of electron plasma in a closed space (diodes and multi-electrode devices) and in open space (studying electron flows in the vicinity of natural and artificial celestial bodies). This research is theoretical. The emitting particles are electrons. Moreover, it is assumed that the emission of electrons occurs in vacuum. The electric field potential on the surface of the emitting bodies is considered constant (the first boundary condition). The second condition is determined by setting the field strength on the body surface. Four types of boundary conditions are considered: 1) fully screened electric field; 2) mono-speed flow from the surface; 3) monoenergetic isotropic flow; 4) the starting particles are distributed according to the Maxwell's law. In the second of the above cases, the desired dependence is found analytically. In the third and fourth cases, the dependences of the electric potential strength are found numerically using the kinetic approach. The calculation results are presented in the graphs.