Achieving uniform and reversible magnesium (Mg) deposition is a critical bottleneck for the practical implementation of Mg metal batteries (MMBs), as uncontrolled nucleation and dendritic growth undermine interfacial stability and cycling performance. To address this, we introduce an atomic-level surface design strategy that guides Mg nucleation through precise interface engineering. To model this concept, we designed a freestanding porous carbon nanofiber framework embedded with Zn single atoms (ZnSA@PCF), derived from pyrolyzed electrospun PAN/ZIF-8 composites. This architecture simultaneously provides high surface area via uniformly distributed hollow nanocages and magnesiophilic Zn single-atom sites that serve as catalytic centers to direct Mg plating. This dual design significantly reduces the nucleation overpotential and enables dendrite-free Mg growth up to 5 mAh cm–2. The theoretical simulation results reveal strong Mg affinity at the introduced Zn SAC sites, while electrochemical tests demonstrate a high critical current density (17 mA cm–2) and ultra-stable cycling over 1500 h with 99.79% coulombic efficiency. This work establishes atomic-level catalyst engineering as a compelling paradigm for interfacial control in next-generation reversible MMBs.