Wet magnesium-ammonia flue gas desulfurization (FGD) process is a promising technology for SO2 removal, while some double salt generated and precipitated in its regeneration system. The XRD and TG/DTG results in present study both indicated the generation of double salt (NH4)(2)Mg(SO4)(2)center dot 6H(2)O in the system. (NH4)(2)Mg (SO4)(2)center dot 6H(2)O was profitable for industrial fertilizers, as well as simplifies the FGD process and reduces energy consumption. Results indicated that lower solubility enabled the easier recovery of (NH4)(2)Mg(SO4)(2)center dot 6H(2)O, and the different molar ratios of ammonium to magnesium ions have no effect on its formation. The optimal precipitation conditions of (NH4)(2)Mg(SO4)(2)center dot 6H(2)O are low pH (acidic condition), reaction for 30 min, low reaction temperature (<= 293 K), and the mole ratio of ammonium to magnesium for 6. Such recyclable method is conducive to guiding the industrial applications for wet magnesium-ammonia FGD technology.