Hydrogen-fueled internal combustion engine (H 2 ICE), along with fuel cells, can play an important role in the expansion of hydrogen infrastructure. However, due to the high-temperature during the combustion process, nitrogen oxides (NOx) are produced, and the low minimum ignition energy of hydrogen can lead to abnormal combustion, such as pre-ignition and backfire, under high-load operating conditions. Therefore, injecting water into the H 2 ICE to reduce the temperature in the combustion chamber can be an effective method to address both issues. However, injecting water into the intake port has the disadvantage of reducing volumetric efficiency after vaporization, so that it is more effective to inject water directly into the combustion chamber. In this study, dual direct injection technology was applied to a hydrogen direct injection system, where water was also directly injected into the combustion chamber, to experimentally implement a method for reducing NOx while improving the highest load. The injection timings and quantities of water injection were varied at 1500 rpm, and the extent of maximum power improvement through water injection was determined under conditions just before knocking occurred. The results showed that the maximum NOx reduction rate through water injection reached 80%, and the highest load could also be improved by 16% with water direct injection.