To understand the variation process of air temperature and pressure in an air cushion surge chamber and its influence on the stress and deformation characteristics of the surrounding rock, based on the water level fluctuation equation and the energy conservation equation, a thermodynamic model for the compressed air in the surge tank considering the effect of heat transfer between air and surrounding rock was proposed, and the rationality of the model was validated. With the thermo-mechanical coupling numerical method of fractured rock mass, the pressure and temperature of the air in the surge chamber were taken as the instantaneous change boundary conditions for numerical simulation, and the stress and deformation characteristics of the surrounding rock of the surge chamber were analyzed. The results show that under the operating conditions of the surge tank, the air pressure and temperature in the surge chamber can fluctuate considerably, resulting in the surrounding rock temperature change accordingly. The temperature distribution of the rock behaves significantly uneven characteristics. The temperature at the joints and fissures has relatively large variation, and larger tensile stress occurs.