A two-dimensional and steady-state model of the vanadium redox flow battery with an interdigitated channel and a thin active electrode was developed to visualize the flow velocity, concentrations of the reactants, and local current distribution in the through-plane direction of the electrode sheets. The concentration overpotential was increased in the low flow speed region. The low mass transport coefficient by a slow flow speed resulted in a higher concentration overpotential. The mass flux distributions at the state of charge of 20% were strongly dependent on the flow speeds due to low bulk concentration of the reactants. Based on the visualized data, not only the reactivity improvement of the electrode material but also the advanced design of the porous electrode structure for a high flow permeability of the electrolyte solution are essential to improve the cell voltage during discharge.