Cutting slope failures along high-speed railways in Northeast China due to snowmelt infiltration were studied using a 3D numerical model. The depth of accumulated snow, daily temperature changes, and freeze-thaw cycles were analyzed. Snowmelt seepage mainly travels about 10 meters into the ground, leading to deep-seated instability with prolonged infiltration and shallow failure with intense, short-duration infiltration. Higher snow depth and temperature changes increase water saturation and pressure, reducing slope stability. Freeze-thaw cycles are more likely to cause slope failure by weakening soil strength and creating cracks. This study helps in designing safer cutting slopes along high-speed railways in cold regions.