Abstract: This study investigates the effects of freeze-thaw (F-T) cycles on the fracture characteristics of sandstone under seasonal freezing conditions on the Qinghai-Tibet Plateau. Laboratory experiments were conducted by pretreating rock samples with F-T cycles in a temperature range of 20°C to -20°C. Impact three-point bending tests were performed using a SHPB system, and the evolution of the fracture process zone (FPZ) was analyzed via high-speed camera recordings and Ncorr digital image correlation software. The results demonstrate that F-T cycles induce internal damage accumulation and mechanical degradation in sandstone. Fracture toughness, peak load, and tensile strength decrease progressively with increasing F-T cycles. As F-T cycles increase, the time required for pre-existing crack propagation extends，the crack opening width within the same time interval decreases, and the time needed to achieve an equivalent opening width increases. Crack opening velocity is significantly suppressed by F-T cycles before 111 ms, with diminished influence afterward, indicating that F-T effects predominantly govern the initial crack tip propagation stage. The FPZ exhibits an "expansion-contraction" two-stage pattern: microcracks initially cluster near the crack tip, and the FPZ expands under increasing load, then contracts and dissipates after main crack propagation due to energy release. F-T cycles promote the formation of distributed pore structures within the rock, enhancing energy absorption capacity. This leads to a reduction in FPZ peak values and an earlier occurrence of peak stresses, accompanied by a transition in failure mode from brittle to ductile, characterized by prolonged crack propagation time and reduced initial opening velocity. The research results can provide basic experimental data reference for the dynamic disaster relief of engineering rock masses in cold regions.