The consequence of digging any underground space is the redistribution of the initial stresses around it. This stress distribution is accompanied by deformation and the creation of joints and cracks around the excavation. In this study, the damaged area caused by tunnel excavation was studied by considering the blasting and mechanized excavation methods, and the parameters affecting its expansion rate (geomechanical parameters of the surrounding rock and in-situ stress) were studied. In this study, a circular tunnel with a diameter of 4 meters and a length of 9 meters was modeled by a numerical method (FLAC3D software). In the numerical model, the tunnel was excavated from a distance of 0 to 6.0 meters by mechanized excavation and from a distance of 6.0 to 9.0 meters by blasting, and the thickness of the damaged area in each was determined. In total, 30 numerical models were built and analyzed. The results of the study showed that the damaged area caused by tunnel excavation is more extensive in the area affected by the blasting method. The research results also showed that increasing the vertical in situ stress causes an increase in the radius of the damage zone in the tunnel walls, and increasing adhesion, the angle of internal friction, and the ratio of horizontal to vertical stress causes a decrease in the radius of the damage zone in the tunnel walls.