Hydrogen produced via proton exchange membrane (PEM) water electrolysis has been considered as one of the most promising alternatives to store and convert energy derived from renewable sources. The acidic environment within the PEM electrolyzer poses challenges to the metal-based electrocatalysts employed in both cathode and anode, necessitating a high level of corrosion resistance. This review provides a comprehensive overview of the emerging graphene-encapsulated metals in catalyzing cathodic and anodic reactions of water electrolysis under acidic media. The two major behaviors occurring at the graphene/metal interface, i.e., the electron transfer and ionic penetration, are systematically discussed owing to the experimental results and computational simulations. The correlation between the graphene shell and underlying metal, as well as their impact on the electron and ion behaviors, is further revealed. The mechanisms governed by the electron and ion behaviors are proposed for graphene encapsulated metal catalysts, providing valuable insights toward the design of cutting-edge metal catalysts for the acidic water electrolysis.