As one kind of hygroscopic salts, potash readily absorbs large quantities of water vapor from air during storage and transportation processes. Accumulated moisture will further penetrate into a potash bed to cause serious caking. To study moisture migration within a potash bed, an experimental test apparatus was constructed to investigate the moisture redistribution of a potash bed. A one-dimensional mathematical model with physically realistic representation of moisture transport processes was developed to simulate moisture migration. Based on Whitaker's theory, a model accounting for vapor diffusion, and liquid film movement by capillarity and gravity effects was fully implemented. An adsorption/desorption model was used to determine the phase change rate. The numerical model is validated using experimental data with a small range of uncertainty for particle sizes that have a small size range. Numerical simulation results show that predictions agree with the experimental results within the 95% uncertainty bounds.