The large deformation of soft rock, which is of obvious creep characteristics, seriously threatens the safe operation of TBM (tunnel boring machine). In this paper we analyze and evaluate the deformation of surrounding rock and the safety of supporting structure in the soft rock TBM tunneling segment of a deep-buried water conveyance tunnel. We also investigate into the creep characteristics of soft rock under high stress conditions and compares the stress states of segment structures supported with different methods. Results demonstrate that the stress state of segment and the safety margin of segment structure can be effectively improved by adopting large cross-sectional expansion excavation in association with a buffer layer consisting pea gravel layer and polyethylene foam plate. We suggest to provide reliable working condition for TBM by selecting suitable expansion excavation section and support method as well as reserving enough space for surrounding rock deformation via targeted rock rheological tests and deformation monitoring for similar deep buried tunnel projects. The research findings offer technical support for smooth tunneling, and also provide reference for the construction of similar ultra-long deep-buried tunnels.