Abstract: In order to investigate the Brazilian tensile mechanical behaviors of high temperature granite and its mesoscopic failure mechanism under different cooling methods, the numerical simulation of tensile mechanical properties of high temperature granite is carried out by using the cohesive thermo-mechanical coupling model with ABAQUS software. The mesoscopic failure mechanism of high temperature granite specimens under different cooling methods is revealed through in-depth analysis of the initiation, expansion and evolution of microcracks during the loading process. The effects of grain boundary length and grain boundary strength on tensile mechanical behavior of high temperature granite are further discussed. The results show that the cohesive thermo-mechanical coupling model could not only solve the problem of temperature transfer between mineral grains, but also effectively simulate the effect of temperature and cooling method on the mechanical properties of granite. With the increase of grain edge length, the tensile strength of granite increases, the proportion of grain boundary cracks decreases and the proportion of transgranular cracks increases, and the control effect of grain boundary decreases. With the increase of grain boundary strength, the tensile strength of granite increases, the number of grain boundary cracks decreases, the number of total cracks and transgranular cracks shows two trends of decreasing continuously and increasing first athen decreasing.