Cutting damages caused by frost action seriously threaten the safe operation of railways in cold regions. This paper uses worth of monitoring data to examine the temperature, unfrozen water, and deformation behaviors of a new High-speed Railway (HSR) anti-frost cutting bed in a deep seasonally frozen ground region. A frost numerical model is established to study the effectiveness of the anti-frost cutting bed under extreme weather conditions. The influence of snow cover on the soil water-heat state and the causes of slope instability in cold regions are also discussed. Results demonstrate that the frost depth of the cutting top is less than that of the cutting center and that the sensitivity of different soil layers’ unfrozen water content to ground temperature changes are delayed in turn. Frost heave mainly occurs in the initial freezing and freeze–thaw alternating periods at the ground surface. Greater infiltration of rainwater or snow melt will lead to a greater peak frost value. Slopes in frozen soil regions are thus prone to instability and collapse at the freeze–thaw interface. These findings will help to improve understandings of thermal-moisture-mechanical behaviors for cutting beds with spatiotemporally in deep seasonally frozen ground regions, thereby potentially improving HSR operation quality.