Plasmon-mediated photocatalysis via hot-electron transfer attracts increasing interest due to its capability to improve energy utilization efficiency. However, more insightful information is still needed to reveal the mechanism of interfacial hot-electron transfer. Herein, the plasmon-induced hot-electron transfer at different plasmonic interfaces, including Au-insulator (SiO₂), Au-semiconductor (TiO₂ and Cu₂O), and Au-metal (Pd and Pt), is directly investigated using surface-enhanced Raman spectroscopy (SERS) and density functional theory calculation with a (sub)nanometer spatial resolution, through the fabrication of well-defined plasmonic nanostructures. (Sub)nanometer-distance dependence of interfacial hot-electron transfer has been identified for the first time. Hot electrons can migrate across the Au-semiconductor or Au-metal interfaces and transfer more than 10 nm in semiconductors but decay to thermally equilibrated states rapidly in metals in less than 1 nm. Such a transfer process is blocked at the Au-insulator interface. This work promotes the fundamental understanding of plasmon-induced hot-electron transmission and photocatalysis at plasmonic interfaces.