<p>Freezing and thawing are characteristics of climatic conditions in alpine regions. We analyzed the deterioration mechanisms of expansive soils under freeze-thaw cycles from three perspectives: microscopic, phenological, and macroscopic. The results of scanning electron microscopy of expansive soil samples revealed that greater moisture content was associated with stronger damaging effects of freeze-thaw cycles on soil; large particles inside the soil were found to break into smaller particles, and the number of mesopores increased significantly. The pore structure evolution laws of expansive soil samples were analyzed, and the results revealed differences between samples with different levels of water content under freeze-thaw cycles. The freeze-thaw cycle aggravates pore development and increases soil moisture damage. Both macroscopic strength and microstructural evolution had a higher degree of deterioration in samples with high water content under freeze-thaw cycles. The study of the change in apparent morphology, microscopic steady state evolution, and macroscopic strength deterioration may provide valuable experimental data for reference in construction in areas with swelling soils.</p>