The one-dimensional diffusion model of leaching was developed on the basis of the Soxhlet-type leaching experiment of waste glass. Emphasis was placed on proposing a model for the growth of surface layers and for an immobilized reaction inside these layers. The equations derived from the modeling were solved numerically and the resulting equations were implemented in a computer code named LEACH. The computed and measured leach rates of sodium, cesium, calcium, and strontium were in good agreement under the Soxhlet-type leaching condition. The computed results revealed that the growth of surface layers, including the immobilized reaction, plays an important role in the leach rates of elements, because the diffusion coefficients of surface layers were much different from those of the bulk glass, and because for calcium and strontium the immobilized reactions affected their leach rates. Therefore, in order to predict the leach rates of waste glasses by using the proposed model, the time dependence of the growth of surface layers should be measured experimentally.