Taking the underground powerhouse of the Dadu River Shuangjiangkou Hydropower Station as a research object, using single-hole acoustic wave tests to investigate the wave velocity attributes of the unloaded perimeter rock post-cavern excavation under high geostress. This evaluation allows us to pinpoint the extent of the Excavation Damage Zone (EDZ) within the perimeter rock and discern its evolutionary patterns under the influences of stress redistribution and proximity blasting, along with understanding the unique traits of the EDZ across varied regions. By leveraging the finite difference numerical analysis method, we probe into the mechanisms of EDZ formation. This approach exposes the implications of blasting load, transient geostress unloading, and stress redistribution on the EDZ of the surrounding rock under high geostress conditions, considering both individual and concurrent effects of these factors. The findings of this research hold significant theoretical and practical merit, offering crucial technical insights for enhancing the safety evaluations.