In this paper, chemical composition, mineral composition, thermal properties, microstructure and binding characteristics of hemi-hydrate phosphogypsum were studied. The results showed that the chemical composition of hemi-hydrate phosphogypsum mainly consists of CaO and SO₃(up to 70% by mass), with a small amount of crystal water and P₂O₅. The hemi-hydrate phosphogypsum has radioactive elements, which meet the requirement of GB/T6566-2010 Limit of radionuclides in building materials. Mineral composition of hemi-hydrate phosphogypsum is mainly bassanite, whose exothermic peak is weak. Hemi-hydrate phosphogypsum is almost in aggregation made of irregularly oriented calcium sulfate crystals, and its binding characteristics are poor, with dry strength being 0.38 MPa. There exists difference between hemi-hydrate phosphogypsum and bassanite prepared by gypsum as raw material, and hence the direct application of hemi-hydrate phosphogypsum to building materials needs further study.