<p>With respect to underground engineering, activities involving the mining of mineral resources, coal is found in a complex environment, in which temperature, gas, and external loads combine. In order to explore damage deformation, including energy transformation mechanisms in coal under different failure conditions, a triaxial compression test at different temperatures, and at different gas pressures was carried out by using triaxial servo-controlled seepage equipment of thermo-fluid–solid coupling. Based on this test, when the influence of thermal damage is examined, the whole damage change equation of coal under different temperatures and external loads might be obtained. Moreover, a damage constitutive model for coal at different temperatures, and under different gas pressures was established by considering the degradation of coal’s mechanical properties caused by gas pressure and temperature. Furthermore, concerning the whole process relating to coal’s deformation and destruction under complex stress, an unstable phenomenon driven by energy, including energy’s build-up, and dispersal that shows coal damage and instability is exhibited. Therefore, a mathematical expression of energy, based on damage and deformation of coal rock, that examined the effects of temperature and gas pressure, has been obtained in this paper. The results revealed the various stage characteristics in the deformation and disintegration process that were, basically, similar under different temperatures and gas pressures. Temperature and gas pressure possess a greater impact on coal’s mechanical properties than other factors. Secondly, a damage constitutive model for coal under different temperatures and gas pressures was established in order to consider the degradation of coal’s mechanical properties caused by temperature and gas pressure. In addition, by considering the influence of temperature and gas pressure, the mathematical expression of energy dissipation, based on coal damage and deformation, was obtained, where it was found that the whole process relating to coal damage deformation was accompanied by a continuous dispersal of energy.</p>