Electrolysis of water, especially alkaline water electrolysis (AWE), is the most promising technology to produce hydrogen in industry. However, only 4% of the total hydrogen is produced in this way because the electrode materials are expensive, inefficient, or unstable. Here, it is reported that the large-scale 3D printed martensitic steel (AerMet100) can be the bifunctional electrode for AWE with high catalytic performance, which may dramatically increase the green-hydrogen percentage in the market and provide strategic planning for energy management. It is found that the martensitic steel by fast anodization (3 min) can realize ultra-high hydrogen and oxygen evolution reactions (HER and OER), and excellent stability at high current densities. Particularly, this electrocatalyst shows a low overpotential of 3.18 V and long-term stability over 140 h at 570 mA cm in overall water splitting. Additionally, the treated large-scale steel can work well under a very high current up to 20 A. This study demonstrates that martensitic steel can be commercialized as a highly efficient catalyst for industrial hydrogen production in AWE, which should provide solutions to the energy crisis and environmental pollution.