When designing a redox flow battery system, compression of battery stack is required to prevent leakage of electrolyte and to reduce contact resistance between cell components. In addition, stack compression leads to deformation of the porous carbon electrode, which results in lower porosity and smaller cross-sectional area for electrolyte flow. In this paper, we inves-tigate the effects of electrode compression on the cell performance by applying multi-dimensional, transient model of all-vanadium redox flow battery (VRFB). Simulation result reveals that large compression leads to greater pressure drop through-out the electrodes, which requires large pumping power to circulate electrolyte while lowered ohmic resistance results in bet-ter power capability of the battery. Also, cell compression results in imbalance between anolyte and catholyte and convective crossover of vanadium ions through the separator due to large pressure difference between negative and positive electrodes. Although it is predicted that the battery power is quickly improved due to the reduced ohmic resistance, the capacity decay of the battery is accelerated in the long term operation when the battery cell is compressed. Therefore, it is important to opti-mize the battery performance by taking trade-off between power and capacity when designing VRFB system.