Abstract: With the westward shift of coal resource exploitation in China, water-rich and weakly cemented sandstone strata have emerged as a major geotechnical challenge in deep coal mining. However, systematic investigations remain scarce regarding the dynamic response mechanisms of unfrozen water in such low-strength, water-sensitive rock under deep multi-field coupling conditions. In this study, sandstone samples collected from the Suboergai mining area in the Ordos Basin were examined to elucidate pore structure evolution, unfrozen water distribution behavior, and nuclear magnetic imaging characteristics. The results indicate that: (1) During the freezing stage, pore water in all three sandstone types solidifies sequentially as “free water → capillary water → adsorption water”, whereas thawing follows the reverse order “adsorption water → capillary water → free water”. (2) Nuclear magnetic resonance imaging reveals that pore water in fine-grained sandstone is mainly enriched in the lower-T? region, with no supercooling effect observed, and the final unfrozen water content reaches 3.08%. Pore water in fine-gravel sandstone and siltstone exhibits a central-dominant and a relatively uniform distribution, respectively, both experiencing supercooling (freezing temperature −1.5 to −2 °C), with final unfrozen water contents of 6.69% and 3.37%. The proportion of micro-pores inside the rock is negatively correlated with the freezing point temperature. (3) Freeze-thaw cycling promotes an increase in small- and medium-sized pore throats while reducing large pore throats, thereby accelerating structural deterioration of the rock mass.