The tunneling machine for the Hanjiang to Weihe River Water Diversion Project is expected to encounter complex and unpredictable geological conditions, which could result in accidents such as large deformations of soft rock and segment failure. To address this, a refined numerical simulation model using FLAC3D was utilized to study the coupling mechanism of shield-support-surrounding rock under loess geological conditions. Results show that the overall rock deformation is significant, but due to the support effect of the face, displacement at the cutter head is minimal. Deformation of the surrounding rock increases gradually from the back of the face to the pipe segment. Stress redistribution occurs within a certain range of the gap reserved at the shield, with the maximum principal stress in the secondary stress located near the tail of the shield. A typical cave section of Bailu Tableland exhibits a layered stress distribution phenomenon, with stress release from the cave wall to the outer rock mass. This includes zones of concentration, transition zones, and non-interference zones. In the excavation direction of the tunnel, the maximum principal stress is relatively high at the junction of the shield tail and the segment structure, as well as at the entrance of the tunnel.