To address the degradation of mechanical and durability properties of microcapsule-based self-healing cementitious materials caused by interfacial defects, this study focused on cement mortars containing dual microcapsules of epoxy resin (EP) and tetraethylenepentamine (TEPA) as the study subject. We systematically compared and analyzed the effects of three mineral admixtures — nano-SiO2, silica fume (SF), and ground granulated blast furnace slag (GGBFS) — on the material’s mechanical properties, resistance to chloride ion penetration, resistance to sulfate attack, resistance to carbonation, and freeze-thaw durability, and further elucidated their mechanisms of action. The results indicate that all three mineral admixtures can synergistically optimize the pore structure of the paste through a combination of micro-filling and pozzolanic effects, thereby enhancing the interfacial bonding between the microcapsules and the cement matrix, which effectively improves the mechanical and durability properties of the microcapsule-modified cement mortar. Among them, nano-SiO₂ and SF demonstrated superior performance in enhancing resistance to chloride ion penetration, sulfate attack, and freeze-thaw cycles, while GGBFS showed the most significant improvement in flexural and compressive strengths. Overall, mineral admixtures can effectively compensate for the loss of intrinsic properties in the cement matrix caused by the introduction of microcapsules, providing a theoretical basis and technical support for the engineering application of self-healing cement-based materials.