Abstract: Resistance method was used to test the crystallization metastable zone width of the ammonium persulfate solution. By determination of the thermodynamics data of ammonium persulfate crystallization under different cooling rates，ammonium persulfate supersaturated concentration curves under different cooling rates and the ammonium persulfate crystallization metastable zone width were obtained.Results showed that the supersaturated concentration of ammonium persulfate increased along with the rise of temperature under the same cooling rate.Ammonium persulfate metastable zone width increased obviously in the range of 40~50 ℃.Under different cooling rates，the largest metastable zone width was generally at the cooling rate of 40 ℃/h.This provided theoretical basis for industrial crystallization of ammonium sulfate production.

Key words: ammonium persulfate, crystallization, cooling rate, metastable zone width