Optimal electrode compression can efficiently reduce electrode contact resistance and enhance species mass transfer so that the performance of vanadium redox flow battery (VRFB) is consequently improved. New designs of VRFB with a serpentine flow field on the current collector and compressed thin electrodes are investigated to increase its power density. In this study, the intrusion ratio, porosity, strain–stress, area specific resistance, hydrodynamic characteristics, and charge/discharge performance of VRFBs are comprehensively characterized under different compression ratios (CRs) which can be adjusted by changing the assembly force. Then, VRFBs using carbon felts with different CRs are tested by experiments, and the influence of electrode compression on VRFB cell performance is quantitatively evaluated. The in-homogeneous compression of carbon felt electrode in a VRFB with a flow field leads to a non-uniform porosity distribution of the electrodes under the channel, intrusion, and rib regions. The intrusion ratio, local average porosity, and permeability at different CRs are obtained. The Kozney–Carman constant of carbon fiber felt is modified by measuring the flow pressure drop through the electrode. The charge/discharge curves are acquired and the corresponding energy efficiencies are calculated under different CRs. It is shown that the charge/discharge time increases with the CR, and the energy efficiency can be improved to a maximum of 19.4% when the CR varies from 0.3% to 41.8%.