When the dissociation of ferrous sulfate(FeSO₄) takes place, the reaction mechanism and the composition of carbon that is used as reduction agent for accelerating dissociation were studied. The formation of ferric sulfate(Fe₂(SO₄)₃) occurs in the process of the dissociation of ferrous sulfate. The formation of ferric sulfate always delays the dissociation of ferrous sulfate. The formation of ferric sulfate and the oxidation of SO₂ through the catalytic action of Fe₂O₃ must be avoided to increase the dissociation rate. At this time the ratio of carbon required to prevent this formation is 6% of the sample under the inert condition and the sooner the sample is heated, the better. For the dehydration of FeSO₄·7H₂O and the roasting of FeSO₄ about 2250.8(㎉/㎏·Fe₂O₃) is required at 960℃.