Abstract: Thermal analysis was used in the investigation of reaction process for sulfuric acid production from phosphogypsum. The effects of different raw material C/CaSO4 molar ratios on reaction process and reaction temperature were investigated with TG-DTA thermal analyzer. Through the comparison for the difference between experimental and theoretical weight loss values，it was found that CaSO4 was reduced to CaS by C during the first reaction step when raw material molar ratios was 0.4 and 0.5. At the same time，the reaction temperature decreased with increasing raw material molar ratio. However，the products were CaO and CO，etc. during the first reaction step when raw material molar ratio increased to 0.6. XRD results of samples also confirmed that the reaction resultants included CaS and CaO respectively. Therefore it was concluded that the use of thermal analysis in the investigation of reaction process for sulfuric acid production from phosphogypsum was feasible. Finally a discussion on the reaction mechanism was given.