Abstract: Understanding the moisture migration mechanisms in railway subgrade soils under dynamic slaking (D-S) is critical for elucidating the formation mechanisms of frost heave and mud pumping defects in heavy-haul railways. This study employs an autonomously developed hydromechanical coupled testing system to conduct dynamic slaking triaxial tests on subgrade soils. By analyzing resistivity characteristics, we investigate the moisture migration processes and reveal the underlying mechanisms of dynamic effects on moisture transport. A normalized resistivity-based water content calculation method is established to analyze the coupled interaction mechanisms of dynamic stress and dry density on moisture migration. Key findings include as follows: (1) Soil sample resistivity exhibits a three-stage evolution pattern ("decreasing-increasing- stabilizing") under dynamic slaking, validating the applicability of the hydromechanical coupling testing system for dynamic slaking experiments; (2) With increasing dynamic stress, moisture migration velocity decreases by approximately 11%, while equilibrium water content reduces by about 0.8%; (3) Higher dry density accelerates initial water content growth, with capillary suction phenomena observed in high-density samples, promoting upward moisture migration from the bottom. These findings provide experimental evidence for improving dynamic slaking moisture migration models and advancing the understanding of frost heave and mud pumping pathogenesis in railway subgrades.