Modified phosphogypsum and its preparation

The present invention discloses a modified phosphogypsum and its preparation process. Its main weight composition is formed from 10-30% of additive (one, two or three kinds of aluminium sulfate slag,alum stone, plant ash, bentonite, slag, dickite, waste liquor and waste residue of paper mill and soda plant, white mud and sepiolite) and 70-90% of phosphogypsum. The phosphogypsum and additive are mixed together, and stacked at a certain temp. so as to obtain the modified phosphogypsum. If said modified phosphogypsum is closed-heated at 30-100 deg.C for 8-48 hr., and formed, dried and can be made into the cement retarded, and if the modified phosphogypsum closed-heated for 8-24 hr, is calcined at 600-900 deg.C, and can be made into cement reinforcing agent.