Heterostructures, [1] particularly 2D heterostructures, have shown great potential in the field of catalytic energy conversion due to the fascinating synergism of different components in tuning electronic structures for promoted surface catalysis. [2-5] In typical catalytic reactions, heterostructures always need to be exposed to corrosive liquids and gases to fully interact with the reactants. Therefore, the rational design and synthesis of heterostructures that have rich exposed active sites and highly stable heterointerfaces are rising as an appealing and critical issue in the area of energy conversion. On the other hand, hydrogen generated from electrochemical water splitting is regarded as an ideal alternative to fossil fuels because of its ultrahigh gravimetric energy density, zero-carbon emission, and natural abundance. [6-10] Currently, the alkaline electrolyzers are technically more available for the production of electrocatalytic hydrogen, such as in the water-alkaline electrolysis and in the chloralkaline industry, owing Heterostructures exhibit considerable potential in the field of energy conversion due to their excellent interfacial charge states in tuning the electronic properties of different components to promote catalytic activity. However, the rational preparation of heterostructures with highly active heterosurfaces remains a challenge because of the difficulty in component tuning, morphology control, and active site determination. Herein, a novel heterostructure based on a combination of RuMo nanoalloys and hexagonal N-doped carbon nanosheets is designed and synthesized. In this protocol, metal-containing anions and layered double hydroxides are employed to control the components and morphology of heterostructures, respectively. Accordingly, the as-made RuMo-nanoalloysembedded hexagonal porous carbon nanosheets are promising for the hydrogen evolution reaction (HER), resulting in an extremely small overpotential (18 mV), an ultralow Tafel slope (25 mV dec −1), and a high turnover frequency (3.57 H 2 s −1) in alkaline media, outperforming current Ru-based electrocatalysts. Firstprinciple calculations based on typical 2D N-doped carbon/RuMo nanoalloys heterostructures demonstrate that introducing N and Mo atoms into C and Ru lattices, respectively, triggers electron accumulation/depletion regions at the heterosurface and consequently reduces the energy barrier for the HER. This work presents a convenient method for rational fabrication of carbon-metal heterostructures for highly efficient electrocatalysis.