The effect of the reaction time and the amount of additives on the decomposition rate and temperature of phosphogypsum were studied in the weak reducing atmosphere of 3vol% CO by using the mixture of phosphogypsum and a certain percentage of CaCl2,Fe2O3 and MgO additives.The result shows that the decomposition rate of phosphogypsum reached 85% by adding CaCl2 and Fe2O3,and the decomposition temperature of phosphogypsum was only 950℃ which was 100℃ lower than the one of decomposition reaction of phosphogypsum without any additives.And the addition of MgO had no significant effects on the decomposition of phosphogypsum under the same condition.