The Zr/O/W Schottky-type thermal field emission cathode is a key component in advanced electron beam instrumentation, with its unique interfacial emission mechanism remaining a focus of research in cathode technology. Traditional understanding attributes the decrease of work function at the cathode tip to a monolayer adsorption of Zr-O dipoles on the W(100) facet, with the electropositive orientation directed outward, perpendicular to the surface. This study successfully fabricats a high-performance Zr/O/W Schottky-type thermal field emission cathode that exhibits exceptional emission characteristics, including a current density of 2.5×10⁴ A/cm² and operational stability exceeding 8000 h. Comprehensive microstructural characterization of the activated emission zone is performed utilizing energy-dispersive X-ray spectroscopy (EDS) and Auger electron spectroscopy (AES), thereby precisely determining elemental distribution profiles across both surface and subsurface regions. The results reveal that during cathode preparation, the zirconia coating diffuses in the form of Zr-O complexes within the tungsten matrix, forming nanoscale enrichment zones specifically on the W(100) facet. Under operational conditions combining elevated temperature (1700–1800 K) and high electric field (>10⁷ V/m), the W(100) surface develops not an adsorbed Zr-O dipole monolayer, but a nanoscale Zr/O/W₍₁₀₀₎ composite oxide structure. This multilayer structure consists of three coherently integrated components: 1) an oxygen-enriched diffusion layer beneath the W(100) interface, 2) the crystalline W(100) substrate, and 3) an overlying Zr-O thin film with multiatomic-layer thickness. First-principles calculations simulating the dynamic evolution of the W(100) emission interface during thermal treatment corroborate the experimental findings. The computed work function of the cathode emission surface decreases significantly from 5.02 eV (characteristic of nano-WO₃) to 2.85 eV, showing excellent agreement with experimental measurements. When the emission interface becomes unbalanced due to external perturbations, the continuous diffusion of the zirconia coating toward the tip region, combined with the diffusion of Zr-O complexes from the subsurface of the W(100) crystal plane to the interface, enables autonomous replenishment of surface-active sites. This dynamic process effectively maintains a stable low-work-function emission surface. Both theoretical and experimental evidence consistently demonstrate that the Zr/O/W₍₁₀₀₎ oxide film serves as the fundamental material basis for the exceptional emission current density, remarkable stability, and extended operational lifetime of Zr/O/W cathodes.