The effect of the concentration (0-2.5 mol·kg-1) of ammonium sulfate on the solubility of calcium sulfate dihydrate is measured in inductively coupled plasma-atomic emission spectrometry (ICP-AES) under the conditions of 298.15-348.15 K. The activity coefficient model of extended Debye-Hückel was applied to correlate the experimental data

and the averaged relative deviation were found at 2.81%. Meanwhile

the activity coefficient model of extended UNIQUAC-Debye-Hückel was applied to calculate the solubility of calcium sulfate dihydrate in ammonium sulfate solution

and the experimental data agreed well with the model prediction

with an averaged relative deviation of 4.13%. The theoretical and experimental results show that the solubility of calcium sulfate dihydrate can firstly decrease and then increase with the increasing of the concentration of ammonium sulfate under the conditions of 298.15-348.15 K. At the solubility mutation point the concentration of ammonium sulfate is 0.07-0.08 mol·kg-1 under the synergetic effect of common-ion effect and salt effect. There are strong effects of temperature on the solubility of calcium sulfate dihydrate under higher ammonium sulfate concentrations (0.3-2.5 mol·kg-1). The results provide better understanding and theoretical guidance for process design of CO2 mineralization with phosphogypsum.