Construction of compressed air energy storage caverns in deep, medium-to-soft rocks requires consideration of the strain-softening characteristics of the rock mass, a critical factor that cannot be overlooked in cavern structural design. To improve the predictive accuracy of surrounding rock deformation during cavern operation, a numerical method for the mechanical response of surrounding rock in high-pressure caverns was proposed based on the Hoek-Brown criterion. It is crucial to distinguish between strain-softening mechanisms during the excavation phase and those during the high-pressure operational phase. A stress path for the cavern’s surrounding rock was presented, incorporating the bidirectional strain-softening characteristics of the rock mass. The influence of surrounding rock quality grade and softening degree on the stress path was investigated. Results indicate the following: (1) Stress within the plastic zone of the rock mass correlates closely with its strength values. Compared with scenarios in which strain-softening is not considered, incorporating strain-softening leads to markedly different stress distributions. During the excavation phase, circumferential stresses within the plastic zone decrease, whereas during the high-pressure gas storage phase, these stresses increase considerably. (2) Incorporating strain-softening substantially increases rock mass displacement and considerably expands the plastic zone. The rate of increase in the radius of the plastic zone accelerates during the plastic expansion phase. (3) Rock mass deformation is a critical parameter in the design of high-internal-pressure cavern linings. (4) Therefore, the strain-softening characteristics of Grade Ⅲ or poorer rock masses must be taken into account during the structural design of high-internal-pressure underground caverns.