The aluminum-water reaction for hydrogen production exhibits significant potential in the energy sector due to its low cost and high hydrogen density. However, the great challenge in controlling the kinetics of the aluminum-water reaction hinder the advancement in applications. This study proposes a polymer-encapsulated aluminum nanoparticles (Al NPs) and NaOH nanocomposite coating for on-demand hydrogen production via aluminum-water reaction. By monitoring the coating reaction process using scanning electron microscopy and X-ray diffraction, the results indicate that fibrous AlO(OH) gradually forms on the Al NP surface during the reaction, eventually transforming entirely into bulk Al(OH) 3. Furthermore, by adjusting the size of Al NPs (50-1000 nm) and the hydrophilicity/hydrophobicity of the polymer matrix, the hydrogen production rate can be regulated within the range of 0.23-9.65 mL·s -1·g -1. Finally, multiple interval reactions were adopted to verify the effectiveness of water-controlled on-demand hydrogen production. This strategy overcomes the dependence of aluminum-water reaction on extensive alkali solution, providing new insights for the development of hydrogen production.