In order to evaluate the instability risk of surrounding rock of mountain highway tunnel through soft fracture zone, the stress and deformation characteristics of surrounding rock under the condition of tunnel construction crossing weak fractured zones were studied. The results show that in the process of tunnel excavation, the radial stress and displacement of surrounding rocks show three stages: slow-fast-stable. When the tunnel passes through the soft fracture zone, the radial stress increment of each part of the surrounding rock is higher than that of the homogeneous stratum. Due to the existence of soft fracture zone, the stress release of surrounding rock caused by tunnel excavation is aggravated, which leads to the expansion of the influence range of construction disturbance, so that the deformation of surrounding rock of tunnel in soft fracture zone is obviously higher than that in homogeneous stratum. It is concluded that the influence of soft fracture zone on the mechanical response of surrounding rock should be paid attention to during tunnel construction. According to the differential distribution characteristics of stress and deformation of surrounding rock of tunnel in soft fracture zone, it can provide reference for the design and construction optimization of highway tunnel in weak stratum in mountainous area.