Three models are proposed for the sulfate diffusivity change due to the pore clogging by crystallization from the chemical sulfate attack of cement-based materials. The averaging model takes a linear relationship between the crystallization quantity and diffusivity change while the constriction model takes an inverse linear form and the self-consistent scheme model lies in between. These models are integrated into a diffusion-reaction model for chemical sulfate reactions in cement-based materials and solved numerically. The results show that all the three models can capture the rapid self-deceleration of sulfate ingress by fitting different relative kinetic coefficients k/D0 and reduction parameters θ.