The distribution of water channels in the crystal morphology of type-a hemi-hydrated gypsum (alpha-HH) was theoretically detected to investigate the effect of water channels on the hydration reactivity of hemi-hydrate phosphogypsum( HPG). Results showed that water channels were mainly distributed in the cylinders of alpha-HH crystal, whereas no water channel existed in the conical surfaces parallel to the z-axis. Increasing the number of water channels was critical to enhance the hydration activity of HPG compared with the hydration reactivity of industrial HPG and type-alpha high-strength gypsum. Controlling the technological parameters of crystallization by concentration of liquid-phase SO42- made it possible to obtain HPG which had the stumpy crystals of alpha-HH and high hydration reactivity. (C) 2016 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.