Alkaline water electrolysis (AWE) is a prospective method for producing green hydrogen to solve the energy crisis and reduce environmental pollution. However, the hydrogen production efficiency through this process is exceptionally low because the electrodes are expensive and inefficient. In this work, a kind of high-entropy alloy (HEA), bulk AlCoCrFeNi, is used as the efficient electrode for AWE. Results show that the HEA treated by 5-min fast anodization can achieve ultra-high catalytic activities for hydrogen and oxygen evolution reactions with low overpotentials of 880 and 845 mV to reach the current densities of −500 and 500 mA cm⁻², respectively. For full water splitting, it only needs 3.00 V and exhibits excellent stability of more than 100 h at 500 mA cm⁻². Our study demonstrates that the anodized AlCoCrFeNi HEA has promising applications as a highly efficient catalyst in industrial water electrolysis for hydrogen production, potentially addressing the energy crisis and environmental concerns.