The preparation of alphacalcium sulfate hemihydrates from flue gas desulfurization gypsum was conducted in nonelectrolyte 80 mol% glycolwater solution at 95 ℃ under normal atmosphere. The phase transition is confirmed to be feasibility through the analysis of the solid phase evolution with the time. Trace metal cations K+, Mg2+ can significantly accelerate the conversion rate, while the addition of Fe3+ will slow down the conversion. The alphacalcium sulfate hemihydrate crystals show a shape of shuttle with the addition of K+, but a shape of elongated whisker and flat coin when Mg2+ and Fe3+ are introduced, respectively. The regulation of ion on the conversion rate and the morphology of the products is mainly achieved via its effect on modifying the solution pH and its selective adsorption on crystal surface. This work will promote the development of the technology of the preparation of the alphacalcium sulfate hemihydrates under normal atmospheric pressure in nonelectrolyte alcoholswater solution.