Abstract: The studies on thermal cracking of rock are of important theoretical and engineering application value in geothermal exploration, underground disposal of nuclear waste and oil exploitation. Based on the FDEM-TM method for simulating the thermal cracking of rock, the thermal cracking of a cylindrical specimen under two different temperature boundary conditions is analyzed. The results show that when the inner boundary temperature remains constant and the outer boundary temperature increases (T_r0<T_R0), the outer side of the disc is in the compressed state and the inside of the disc is in the tension state before crack initiation. When the tensile stress exceeds the tensile strength of the material, crack initiates from the inner boundary of the disc and extends to the outside, forming divergent cracks finally. When the outer boundary temperature remains constant and the inner boundary temperature increases (T_r0>T_R0), the inside of the disc is in the compressed state and the outer side of the disc is in the tension state before crack initiation. When the tensile stress exceeds the tensile strength, crack initiates from the outer boundary of the disc and extends to the inside, forming radial cracks from the outside to the inside finally. The simulated results are in good agreement with those of the existing literatures, which further validates the effectiveness of the FDEM-TM method to simulate the thermal cracking of rock.