Abstract: To derive optimum conditions for preparing of ammonium sulphate from phosphogypsum,method of shifting out phosphogypsum and appending dispersant was used to heighten the conversion rate of SO<SUP>2-</SUP><SUB>4</SUB> in phosphogypsum.Response surface methodology (RSM) was used to analyze the effects of mass ratio of materials,temperature,feeding speed,and dosage of dispersant on the conversion rate of SO<SUP>2-</SUP><SUB>4</SUB>&nbsp; in phosphogypsum,moreover prediction models were also established.Optimum conditions were confirmed:mass ratio of calcium sulphate to ammonium carbonate was 1.19,temperature was 44 ℃,feeding speed was 29 g/min,and dosage of dispersant was 1.3×10<SUP>-3</SUP>(mass ratio of dispersant mass in reaction material total mass) via the models evaluator of Matlab software.Corresponding conversion rate of SO<SUP>2-</SUP><SUB>4</SUB> in phosphogypsum under optimized conditions predicted by the models was 96.4%.Experiments proved that the parameters of conversion conditions of phosphogypsum obtained by RSM was viable.