Addressing the longevity issues arising from crack formation in waterproof mortar, this paper innovatively develops a rapid-response self-healing microcapsule with a core composed of magnesium phosphate cement, sodium alginate, and polyethylene glycol, encapsulated within a shell of epoxy resin-complexed ettringite cement. These self-healing capsules, measuring 3-3.5 mm in diameter, exhibit exceptional water resistance and alkaline tolerance, facilitating a tight interfacial transition zone with silicate-based matrices that promotes crack propagation along the capsules. Upon rupture, sodium alginate rapidly swells upon contact with water, forming a hydrogel network within 15 minutes, which expands to over 200% of its original area, thereby achieving initial crack sealing. Subsequently, the magnesium phosphate cement gradually hydrates within this hydrogel matrix, reinforcing the seal over time. Experimental evidence demonstrates that these capsules can repair cracks below 200 μm within three days and those up to 450 μm wide within seven days, with water impermeability recovering to 76% within the same timeframe. This underscores their rapid and efficacious self-repair capabilities, a significant advancement for enhancing the durability of waterproof mortars.