Abstract: The failure mechanism under thermal and mechanical coupling is a key issue for high-level radioactive waste disposal in deep geological rock,and is also the basis for disaster prevention. Based on the uni-axial tension test of granite taken from Beishan region,the authors used three different coupled loading paths to analyze the failure mode of SEM pictures and reveal the characteristics of meso-scale failure. Meanwhile,the law of thermally induced cracking propagation and strain energy is obtained from the simulation of meso-scale sample considering the various materials and distribution. Furthermore the authors establish the relationship between the angle and number of crack,and explain actual porosity evolution with loading stress and different crack angles. The results show that both coupled paths and heterogeneity lead to failure. There is a clear distinction of cracking mechanism between increasing temperature under constant tension.