In view of the fact that most tunnels in Sichuan section of ChengduGuiyang Railway under construction are located in the soft strata of red sand and mudstone, the 1 213 monitoring data of arch settlement and side wall convergence of 407 sections of 10 tunnels are statistically analyzed based on the field measured data. Deformation characteristics and deformation amount of tunnel in weak rock stratum are analyzed. Meanwhile, combined with the analysis of field measured data, the optimization and adjustment of initial support stiffness system for Vclass surrounding rock tunnel in weak red sand and mudstone stratum are numerically simulated under different working conditions. The deformation and stress of different initial supporting structures are analyzed. The results show that the reference value of reserved deformation in the current code for design of tunnel of railway (TB 100032016) is too large. It is suggested that the reserved deformation of shallowburied largespan tunnels (Vclass surrounding rock section) in soft red sandy and mudstone strata should be set at 50-60 mm.