<p>Previous theoretical analyses of deep tunnels have been primarily focused on the deformation of rock mass and stress changes within it. The calculation of support pressure has aligned with that of the limit support pressure, leading to a substantial gap between the theoretical solution and field measurements. This study incorporates the flexible characteristics of support, dynamic construction processes, and softening characteristics of rock mass to propose a new procedure for estimating deformation and support pressure of tunnels excavated in the strain-softening rock mass. Then, the feasibility of this theoretical method is verified through numerical simulation and field monitoring. The analysis indicates that the pressure borne by the support is determined by the motion state of rock mass, rather than its deformation. Within 10&#xa0;m of the excavation face, the proportion of fictitious support force is significant in the total support pressure. Beyond 30&#xa0;m from the excavation face, the pressure shared by the support becomes the primary component of the support pressure. Key factors significantly affecting support pressure include in-situ stress, tunnel radius, GSI, displacement release coefficient, and uniaxial compressive strength of rock. For weak rock mass tunnels, when the rock mass undergoes accelerated motion, strengthening advanced support can decrease pre-deformation to reduce the pressure borne by the support. These findings provide theoretical guidance for predicting support pressure during tunnel construction.</p>