In this paper, fuel velocity distribution nonuniformity among channels in planar SOFC units under different working conditions is numerically investigated. A comprehensive three-dimensional electrochemical model is validated and then adopted in a cell unit model with structure of a real cell unit. The model couples interdependent process of species transport, heat transport, chemical reaction, electrochemical reaction, ionic conduction and electronic conduction. A nonuniformity index is proposed to quantitatively evaluate nonuniform degree of fuel velocity distribution among channels in the planar SOFC unit. The effect of the fuel velocity distribution nonuniformity on cell performance and the effects of working voltage, flow rate, flow pattern and fuel type on fuel velocity distribution nonuniformity among channels are investigated. The result shows that an increase in fuel velocity distribution nonunifomtiy can lead to a cell performance drop and fuel velocity distribution is less uniform under lower cell voltage, lower flow rate, using co-flow configuration instead of counter-flow or using syngas as fuel instead of hydrogen. In addition, the CO oxidation should be considered when studying the fuel velocity distribution nonuniformity among channels. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.