The treating scheme of collapse of surrounding rock of Grade Ⅳ of a large crosssection railway tunnel is described. The distance between collapse cavity and the tunnel is predicted and detected according to collapse volume; and the vertical stress on the primary support structure of the tunnel induced by rock and soil is calculated. The bearing internal force of the primary support structure of the tunnel is simulated by means of ANSYS software and loadstructure model; and the safety evaluation of the primary support structure of the tunnel is made according to Code for Design of Railway Tunnel. Finally, rational primary support structure is adopted and safe construction technologies for collapse section are provided.