In order to study the influence of peripheral hole insertion angle on tunnel blasting excavation over-excavation, relying on the Tong'an high-speed Banyue Mountain Tunnel Project, a three-dimensional numerical model with peripheral hole external insertion angles of 3°, 4°, and 5° was established using ANSYS/LS-DYNA software. After numerical simulation calculation, the relationship between surrounding rock damage and effective stress and the size of peripheral hole external insertion angle was analyzed. The results show that with the increase of peripheral hole insertion angle, the amount of over-excavation also increases, and the over-excavation of the rock body exceeds 15 cm at the insertion angle of 4° and 5°. When the insertion angle is larger than 4° and 5°, the effective stress of the rock body exceeds the strength of the rock body. Based on the analysis of the damage to the surrounding rock and the effective stress, the insertion angle of the peripheral hole should not be larger than 4°.