Aiming at the problem of large deformation such as floor heave and rib spalling caused by conventional bolt and cable support in soft rock roadway, this paper constructs a mechanical model of stress distribution in surrounding rock of roadway, and reveals the pressure relief mechanism of large-diameter pressure relief boreholes in the side by expanding the plastic zone of surrounding rock and transferring the peak stress. The numerical simulation method is used to analyze the influence of key parameters such as drilling depth, aperture and row spacing on the stress transfer and distribution characteristics of surrounding rock. The reasonable parameters of large diameter pressure relief drilling are determined, and the overall control effect is improved by combining active reinforcement support measures. The results show that the large-diameter borehole can effectively expand the plastic zone of surrounding rock and promote the stress peak to transfer to the deep part, and the stress concentration area is mainly distributed on both sides of the borehole. As the pore size increases, the pressure relief effect gradually increases, but the pore size is too large to cause excessive pressure relief; if the drilling row spacing is too small, it is easy to cause local stress concentration, and if the row spacing is too large, the pressure relief effect will be weakened. With the increase of drilling depth, the decrease of stress peak and the transfer distance increase. Through comprehensive analysis, it is determined that the reasonable parameters on site are 160 mm of aperture, 10 m of hole depth and 1.5 m of row spacing. The engineering application results show that after the control technology of ' pressure relief drilling + support reinforcement ' is adopted, the deformation of the two sides of the roadway is reduced by 60.8 %, the deformation of the roof and floor is reduced by 50.3 %, and the stability of the surrounding rock is significantly improved. The research results can provide theoretical basis and technical reference for pressure relief design and surrounding rock control of soft rock roadway.