In order to better interpret the thermomechanical coupling of solid propellant (in this case, HTPB propellant) under cyclic loading, a series of experiments have been accomplished by monitoring the mechanical and thermal responses of tested specimens under constant room temperature. The results reveal that the area and shape of the hysteresis loop, the dynamic loss with increasing cycles and the fatigue lifetime of investigated HTPB propellants were closely related to the self-heating effect accompanying the cyclic loading, which was supported by the detection of the rapid rise in the surface temperature of specimens. Moreover, the results indicate that the self-heating effect was highly strengthened by increasing applied strain range and frequency. Finally, a comprehensive analysis of the correlation of accumulated energy and heat dissipated to the environment was implemented by the heat diffusion equations within the framework of irreversible thermodynamics. To further this work, a thermally coupled nonlinear viscoelastic model is being developed to describe and predict the experimental observations and data. Some results of numerical simulation will be presented.