Calculations of electric field inside a flow-by porous electrode usually involve the assumption that the distribution of geometrical current density along the direction of solution flow inside the electrode is uniform. In the present work we propose the version of its successive refinement without using a priori assumptions. It is demonstrated that the assumption of the uniform current distribution along solution flow is quite acceptable under the conditions of the small changes of polarization resistance at the boundary between the porous electrode and the solution (small current density, high flow rate or prevalence of the side reaction of hydrogen evolution). Quite contrary, in the case of a sharp change of polarization resistance along solution flow this assumption is not fulfilled and causes quantitative distinctions of the spatial distribution of potential, current and concentration inside this electrode. An increase in non-uniformity of overall current distribution with an increase in solution depletion degree inside the porous electrode was confirmed experimentally for copper electrodeposition as an example. (C) 2015 Elsevier B.V. All rights reserved.