<p>Thermal cracking mechanism is an important topic for better understanding the strength and deformation behavior of rock in high-temperature-associated engineering. To investigate the crack propagation and stress evolution in marble under thermal–mechanical condition, a thermal–mechanical coupling model is developed in a grain-based model (GBM) using distinct element method (DEM). The developed GBM is first verified by comparing results derived from Fourier’s law of heat conduction. The micro-parameters in GBM are then carefully calibrated to match a large amount of macroscopic properties obtained from laboratory test. At last, the calibrated model is utilized to simulate the cracking behavior of a marble model under both thermal and mechanical loadings. The results show that as temperature in the treatment increases, the change in the number of thermally induced cracks exhibits a consistent trend with the variation of strength parameter in the model. In the thermal loading process, grain boundary tensile cracks are dominant among the generated cracks, accounting for more than 85%. The intra-grain tensile cracks gradually increase as the treatment temperature increases. In the mechanical loading process, the failure is tensile-shear mixed mode in thermally damaged model, and shear ratio in the failure mode gradually decreases as the treatment temperature increases. The thermally damaged model exhibits a lower vertical stress and a slower crack propagation rate during the initial loading stage when compared to the results of unheated model. Both the number of micro-cracks and the vertical stress slowly increase during the initial loading stage as the treatment temperature increases. However, as the peak stress is approached, the growth of both micro-crack quantity and vertical stress progressively diminishes. The results in this study improve our understanding of thermal damage mechanism in marble.</p>