Abstract: Phosphogypsum is a large?鄄scale industrial solid waste discharged from the wet?鄄process phosphoric acid industry. With the production of the phosphoric acid industry，a large amount of phosphogypsum needs to be harmlessly treated or utilized.It is one of the comprehensive utilization ways to use it to produce cement retarder.But it contains harmful elements such as water?鄄soluble phosphorus and fluorine，therefore，it is necessary to add other substances to modify it.The effect of modification process conditions on the modification effect was studied.The results showed that in the reaction of calcium carbide slag modified phosphogypsum，the reaction time and the adding amount of calcium carbide slag had a great influence on the modification results，while the reaction temperature had little influence compared with reaction time and adding amount.When the reaction time was up to 2 h and the adding amount of calcium carbide slag was more than 0.3%，the soluble phosphorus and fluorine in the phosphogypsum could be effectively removed，which met the performance requirements of the gypsum gypsum in Industrial By?鄄product Gypsum Used in Cement，GB/T 21371—2008.

Key words: carbide slag；phosphogypsum；cement retarder；phosphorus；fluorine