The density functional theory has been used to investigate the methanol adsorption, decomposition and oxidation as well as the water adsorption and decomposition on the clean and Pt-encapsulated Al12N12 cages. It is shown that platinum metal atom can be encapsulated within the Al12N12 cage, thus forming Pt-encapsulated Al12N12 cage electrocatalyst. According to the reaction results, CH3OH and H2O both prefer to be adsorbed on the Al atom top site. The O–H bond scission is the significantly more favorable reaction pathway than C–O bond scission on the cage surface. Furthermore, the structures of the intermediates, transition states and products, the corresponding energy barriers and reaction energies are confirmed. The results also show that the adsorption energies and energy barriers of CH3OH and H2O dissociation are cut down slightly with the aid of the platinum atom. Nevertheless, Pt-encapsulated Al12N12 cage makes the potential energy surface changes smoother than pure Al12N12 cage.