<p>When subjected to sustained high temperatures, the structure of the continuous China railway track system (CRTS) II railway track is susceptible to internal axial pressure, leading to joint damage and the potential for upwarp buckling of the track slab. This study employs model testing to derive the upwarp buckling deformation curve of the track slab under conditions of joint damage. An analytical expression for the upwarp buckling equilibrium path of the track slab is derived through the application of the energy principle. Validation of the outcomes is performed by the comparison with experimental data. The effects of initial upwarp amplitude, initial upwarp curve type, elastic modulus, thickness, and gravity load on the upwarp buckling response of the track slab were investigated. The results show that: 1) The upwarp deformation of the track slab in the narrow joint damage state is concentrated in a minor range on both sides of the joint, forming an inverted ‘V’ shape with concave ends. 2) The joint damage can significantly reduce the upwarp buckling critical temperature rise of the track slab. 3) The magnitude of the initial upwarp amplitude dictates the buckling mode of the track slab, while the initial upwarp curve predominantly influences the upwarp buckling critical temperature rise. Notably, an initial upwarp amplitude below 6.5 mm ensures the buckling resistance for up to a 60 °C temperature rise. 4) The increases in elastic modulus, gravity load, and track slab thickness can increase the upwarp buckling critical temperature rise. As the initial upwarp amplitude increases, the influence of these factors on the upwarp buckling critical temperature rise of the track slab gradually diminishes.</p>