Starch particle digestion is an important topic in food digestion research. This study has developed a diffusion-reaction model to characterize hindered enzyme diffusion and substrate hydrolysis on the surface and in the interior of porous starch particles. A moving boundary numerical method is applied to account for particle shrinkage caused by surface reaction. This model has been proven to predict the digestion rate of various starch particles of different sizes. The parameter estimation procedure quantifies the properties that are hard to measure by experimental techniques, i.e., diameter, reactive area, and proportion of pores accessible for enzyme as well as susceptibility of starch to enzyme. This work formulates a quantitative procedure for identifying the particle digestion pattern (i.e., outside-in or inside-out) by resorting to the developed model. Computational experiments indicate that in addition to the internal architecture, particle size also has a significant effect on the digestion pattern.