In this study, the crystallization process of type-α hemihydrate calcium sulfate (α-HH) in the hemihydrate wet-process phosphoric acid production was simulated. The crystallization induction time of α-HH was determined by monitoring the turbidity changes in 95 ℃, supersaturation from 1.64 to 2.10, 30%P2O5 phosphoric acid solution with different F- and SiF2-6 concentration. The critical nucleation radius and nucleation rates of α-HH were calculated by classical nucleation theory equations, and the effects of F- and SiF2-6 on the crystallization process of α-HH were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that with the increase of F- and SiF2-6 concentration, the crystallization induction time, the surface energy, and the critical nucleation radius of α-HH crystals increase, but the nucleation rates of α-HH crystals decrease. When 0.06 mol·L-1 F- is introduced in the system at the supersaturation 1.64, the crystallization induction time of α-HH crystals is prolonged by 465 s and the nucleation rate is reduced to 0.403×1029 crystal nuclei·cm-3·s-1. However, in the presence of 0.06 mol·L-1 SiF2-6, the crystallization induction time of α-HH crystals is prolonged by 710 s, and the nucleation rate is reduced to 0.339×1029 crystal nuclei·cm-3·s-1. The effect of SiF2-6 on nucleation inhibition of α-HH crystals is greater than that of F-. The F- and SiF2-6 hinder the growth of α-HH crystals along the C-axis, resulting in a decrease of the crystal aspect ratio and a change of the crystal morphology to short cylinder shape. F- and SiF2-6 affect the intensity and crystallinity of α-HH crystals (200), (310), (400) crystal planes. The concentration levels of F- and SiF2-6 in the semi-aqueous wet phosphoric acid are controlled to obtain short columnar α-HH crystals, which are favorable for filtration and washing.