Abstract: To investigate the reinforcement mechanism of gas hydrate cementation on the damage characteristics and structural stability of coal under loading, an in-situ testing apparatus for mechanical properties of gas hydrate-bearing coal was employed. Conventional triaxial loading tests were conducted at confining pressures of 12, 16, and 20 MPa on coal samples before and after gas hydrate cementation. Based on energy calculation principles, this study characterized the evolution of mechanical properties and structural stability parameters during damage progression in coal under loading—both pre- and post-cementation—clarifying the reinforcement mechanism of gas hydrate cementation on coal damage and stability. The results demonstrate that: Both pre- and post-cementation coal exhibit strain-hardening behavior in deviatoric stress-strain curves, with enhanced hardening observed after cementation. These curves consistently feature three stages: elastic, yielding, and strengthening. Energy evolution patterns align with these stages, showing progressive increases in total energy, elastic energy, and dissipated energy with axial strain. Coal undergoes three distinct damage stages under loading—elastic deformation, stable crack propagation, and unstable crack propagation—both pre- and post-cementation. Elastic deformation corresponds to low deterioration (blue warning level), while stable and unstable crack propagation stages exhibit moderate deterioration (yellow warning level). Post-cementation, cohesion, elastic modulus, crack initiation stress, damage stress, and peak strength increase under all confining pressures, with all increases exceeding 22.41%. This confirms gas hydrate cementation effectively enhances coal’s resistance to deformation and failure. After cementation, total energy, elastic energy, and dissipated energy at crack initiation stress, damage stress, and peak stress increase across all confining pressures (maximum increase: 58.14%), indicating significantly improved energy absorption/storage capacity and damage resistance. Post-cementation critical instability stress increases by 18.17%–50.85%, while the modified brittleness index coefficient decreases by 17.14%–33.75% under varying confining pressures. This demonstrates gas hydrate cementation enhances critical instability stress and ductility, thereby strengthening structural stability. The revealed reinforcement mechanisms governing coal damage, failure, and instability through gas hydrate cementation provide critical insights for stability analysis in deep high-gas coal mining, coal degradation laws, and disaster prevention strategies.