Abstract: [Objective] To investigate the disaster-causing mechanism, dynamic evolution process, and post-disaster stability trend of the reactivation of the Huangci No. 2 landslide in Heifangtai, Gansu Province on December 10, 2025. [Methods] Field surveys and the Transient Electromagnetic Method (TEM) were comprehensively applied to analyze the deep structure of the landslide. A back-analysis was conducted based on Massflow numerical simulation, and the 3D limit equilibrium method was utilized to perform quantitative stability evaluation for the post-disaster deposit and the high-steep rear wall. [Results] (1) The landslide reactivation is the result of toe excavation, long-term irrigation, and special meteorological conditions. The freezing-induced water retention effect acted as the direct trigger, where surface freezing blocked seepage channels, causing an accumulation of pore water pressure and inducing a loess-mudstone bedding slide. (2) The entire sliding process lasted for 22 hous, with a cumulative displacement of 310 m. The Massflow analysis reproduced the four-stage evolution process of "creep-acceleration-deceleration-consolidation", and the IoU of the deposition morphology reached 85.85%. (3) Quantitative calculations shows that the current deposit has a safety factor greater than 1.15, indicating a stable state of settlement and consolidation; however, under extreme saturation conditions, the potential collapse volume of the high-steep rear wall could reach 40.9×10⁴ m³, with a maximum sliding distance of approximately 640 m. [Conclusion] The analysis suggests that the reactivation of the landslide is controlled by freezing-retained water and multiple disturbance mechanisms. Although the main body has currently stabilized, secondary instability of the high-steep rear wall is highly likely to occur, necessitating the establishment of a long-term dynamic monitoring system to strictly prevent high-position disasters. [Significance] The understanding of the reactivation mechanisms of loess landslides in seasonal freeze-thaw zones was deepens, providing a scientific basis and technical support for prevention and mitigation of such landslides.