<p>Repurposing the interfacial strain from a hindrance to synergism empowers critical advances for magnetoelectric composites in the application of next-generation energy storage and electromagnetic devices, by reconstructing the interfacial activity and local field distributions. However, its deterministic creation, pivotal for optimizing interfacial electron transport and emergent functionality, is impeded by the uncontrollable atomic distortion and arrangement. Here, we report an oriented-diffusion strategy that tailors interfacial strain by orchestrating atomic migration within a carbon-confined Fe₃C/ZnO magnetoelectric heterointerface. Engineering the outward effusion of dielectric ZnO generates a progressive strain gradient, driving a transition in the interfacial strain from compressive to tensile prior to eventual relaxation. This programmed strain state reconfigures atomic-scale electric fields at the heterointerface, thereby enhancing electron transports and interfacial polarization properties. Consequently, this enhancement enables the strain-mediated metamaterial outperforms conventional electromagnetic absorbers, exhibiting an ultrabroad effective absorption bandwidth covers the wireless communication and radar stealth spectra (2.0-18.0 GHz) with an over 95% radiation reduction. These findings provide a novel perspective on deciphering strain-polarization coupling mechanism and guide the development of advanced broadband magnetoelectric functional materials.</p>