To investigate the sulfate corrosion resistance of cast-in-place repair concrete incorporating recycled coarse aggregate (RCA) under partially exposed conditions, cast-in-place repair concrete specimens with different RCA contents (0%, 30%, and 50%) were immersed in Na₂SO₄ solution. The study systematically investigated the changes in apparent morphology, dimensions, mass, and mechanical properties of the specimens under sulfate corrosion. SEM, XRD, TG/DTG, and MIP were used to characterize the microstructure and mineral composition of the specimens at different corrosion ages. Results indicate that RCA cast-in-place repair concrete partially exposed to a sulfate corrosion environment undergoes coupled physical and chemical corrosion, and the interfacial zone between the recycled aggregate concrete to the base concrete represents the most vulnerable region in the composite system. Incorporating 30% RCA can effectively reduce the degradation rate of specimens under sulfate corrosion, enhance the compactness of the bonding interface, and optimize the interfacial bond strength, compressive strength, and pore structure of the specimens. Excessive RCA content disrupts the internal pore structure, accelerates sulfate ion ingress, and weakens the interfacial bond strength. The presence of RCA significantly reduces the interfacial shear strength of the specimens. After 360 days of sulfate corrosion, specimens featuring 30% and 50% RCA contents exhibit a reduction in shear strength of 15.91% and 40.0%, respectively, compared with the 0% RCA content specimen. Research findings provide a theoretical basis for the application of RCA in concrete repair engineering.