An activity gradient carbon felt (AGCF) electrode is prepared by a simple thermal oxidation method, which is composed of both a low activity electrode near the inlet side and a high activity electrode near the outlet side. The vanadium redox flow battery (VRFB) full cell with AGCF electrodes shows higher discharge capacity (18.7 Ah L−1) and coulomb efficiency (93.6%) than non-gradient carbon felt electrodes (14.3 Ah L−1, 88.4%) at a current density of 80 mA cm−2. From the computational analysis, the AGCF electrodes exhibit reduced overpotential results as well as improved uniform activity at low reactant concentration condition during charging and discharging at the current density. These results suggest that the AGCF electrode is an effective electrode design for high-performance VRFB featuring high energy density by improving electrolyte utilization as well as high roundtrip efficiency by improving energy efficiency.