Abstract: In order to understand the relationship between the deformation of surrounding rocks and the surround? ing rock pressure under large deformation of soft rock to provide basis for yielding design of large deformation, the maximum compressive stress of the elastic supporting structure after some deformations of a single-track railway tunnel without support is calculated by FLAC3D numerical simulation software, the surrounding rock pressure is identified indirectly, and the curve of surrounding rock pressures varying with time is obtained. The monitoring data of some similar projects are compared with this relationship curve, and the results show that: the pressure release curve is divided into three parts, i.e. steep drop area, adjustment area and slow dropping area; the large deformation of soft rock can be divided into convergence type and non-convergence type, it is economical and reasonable if the measur? able peripheral deformations can be controlled within 15 cm (3% of tunnel radius) in condition of convergence, and the best effect can be obtained by installing conventional systematic anchor bolts; the pressure release effect of surrounding rocks will be improved further when the measurable peripheral deformation is more than 63 cm（14% of tunnel radius）in condition of non-convergence; it will result in large increase of plastic zone if the pressures of surrounding rocks are reduced by large peripheral deformations, and the systematic anchor bolts play little role at this time.