In view of the severe freeze-thaw damage and destruction of red sandstone in the cold and high-altitude environment of the Qinghai-Xizang Plateau, red sandstone samples with good integrity from the southeastern part of the region were selected as the research object. Multi-scale experimental methods, including freeze-thaw cycling tests, uniaxial compression tests, nuclear magnetic resonance testing, and quantitative analysis of apparent cracks, were adopted to reveal the coupled evolution laws of the physical and mechanical properties and pore-fracture damage of red sandstone under freeze-thaw action. The results indicate that as the number of freeze-thaw cycles increases, the phenomenon of particle shedding occurs on the surface of rock samples; the dry mass of samples decreases; the porosity increases linearly, and the saturated longitudinal wave velocity shows an exponential attenuation trend. The uniaxial compressive strength and elastic modulus of red sandstone decrease with the increase in the number of freeze-thaw cycles, and the deterioration rate accelerates after 70 freeze-thaw cycles. The transverse relaxation time spectrum of red sandstone shows a three-peak distribution. With the increase in the number of freeze-thaw cycles, the proportion of large pores (＞4 μm) in red sandstone increases linearly, while the proportions of small pores (＞0.1-1 μm) and medium pores (＞1-4 μm) decrease overall. Under freeze-thaw action, the rock damage gradually evolves from the microscale to the macroscale. Within the first 30 freeze-thaw cycles, the main manifestation is the expansion and connection of micro-pores, and after 30 cycles, the development of macroscopic cracks can be observed, eventually leading to rock cracking and failure. A total damage variable for sandstone is proposed by combining the elastic modulus, the volume proportion of large pores, and the fracture rate, achieving a cross-scale definition of the damage variable, which provides a theoretical basis for further understanding the freeze-thaw deterioration mechanism of sandstone in the cold and high-altitude environment of the Qinghai-Xizang Plateau.