In the process of using LNG underground storage, the surrounding rock will be subjected to long-term low-temperature effects, which can induce tensile stresses and frost heave forces, leading to the initiation and propagation of fractures within the rock mass, thereby causing damage and deterioration to the storage facility. To investigate the influence of low temperature on the mechanical properties of the surrounding rock, this study selected coarse and fine-grained granite and conducted Brazilian splitting tests under different low-temperature conditions to study the impact of low temperature on the tensile strength of granite with different particle sizes. The development of cracks in the granite of different particle sizes under low temperatures was analyzed from a microscopic perspective using scanning electron microscopy. The research findings indicate that both coarse and fine-grained granite exhibit a non-linear increase in tensile strength with decreasing temperature. For both types of granite, at temperatures of −30 ℃ and −20 ℃, the complete freezing of pore water enhances the interlocking capability between mineral particles, resulting in a higher tensile strength in the saturated state compared to the dry state. Regardless of the state, the fine-grained granite consistently demonstrates a higher tensile strength than the coarse-grained granite due to its lower heterogeneity. The threshold temperature at which the tensile strength of granite stabilizes is −40 ℃. As the temperature decreases, the fracture mode in granite transitions from intragranular cracks to transgranular cracks and intergranular cracks, resulting in increasing levels of damage. These research findings can provide valuable insights for the evaluation and control of rock mass stability in cavernous LNG underground storage projects.