<p>The interplay between displacement defects governs the evolution of irradiation damage in materials and is of great fundamental interests with important practical implications, from microelectronics industry to advanced nuclear system. Hydrogen, a ubiquitous impurity, is known to segregate to vacancies, but its role in altering vacancy-interstitial recombination—the key process underlying defect annihilation—has not been established. Here, using tungsten as a model system, we show that hydrogen adsorption on the inner surfaces of vacancy clusters significantly suppresses recombination with self-interstitial atoms, thereby inhibiting defect annihilation. We identify a stress-mediated mechanism in which hydrogen adsorption transforms the local stress field of vacancy clusters, weakening their long-range attraction to self-interstitial atoms. Based on this mechanism, we develop a predictive model that quantitatively relates the relative reduction of recombination radius to the hydrogen inner surface density, independent of cluster size. By integrating atomistic parametrization with multiscale simulations, we investigate the co-evolution of hydrogen and displacement defects, which show quantitative agreement with recent experiments, including the hydrogen isotope retention, distribution and desorption. Our results establish a direct link between impurity-defect interactions and defect-defect recombination, providing a physically grounded framework for understanding and controlling irradiation damage in structural materials.</p>