<p>Fe–Cr-based alloys are core candidate materials for fusion reactors and are prone to spinodal decomposition during long-term service, forming Fe-rich <i>α</i> phase and Cr-rich <i>α</i>′ phase, thereby significantly enhancing the strength of the alloy. However, while numerous studies have systematically revealed the kinetic laws and static microstructural evolution characteristics of spinodal decomposition in Fe–Cr alloys, there remains a lack of systematic atomic-scale characterization and in-depth analysis of the microscopic evolution mechanisms linking spinodally decomposed microstructures, dislocation behavior, and strength during deformation. In this work, molecular dynamics simulations were employed to perform tensile tests on Fe–Cr alloys with varying degrees of spinodal decomposition, and systematic analyses were carried out on stress–strain curves, dislocation evolution, local strain, von Mises stress fields, and shear bands. The results show that a large number of mixed dislocations pile up at the α/ α′ phase interfaces and evolve into continuous dislocation networks, which significantly impede further dislocation glide and thus effectively enhance the strength of the alloy. Moreover, due to the competitive interplay between the volume fraction of phase interfaces and the size of the <i>α</i>′ phase, spinodal decomposition cannot continuously enhance the strength of Fe–Cr alloys. Continuous shearing of the <i>α</i>′ phase by dislocations causes fluctuations in the steady stage of the stress–strain curves. Furthermore, localized shear deformation occurs during deformation of the spinodally decomposed Fe–Cr alloy, and the resulting shear bands exhibit discontinuous characteristics owing to obstruction by the <i>α</i>′ phase. This study clarifies the microstructural evolution process of Fe–Cr alloys during deformation following spinodal decomposition and provides a theoretical framework for a deeper understanding of the strengthening mechanisms associated with spinodal decomposition.</p>