The utilization of dry flue gas desulfurization (FGD) residue has become an environmental issue in China. A new method is introduced here to produce sulfoaluminate cement using the dry FGD residue and fly ash without modification of the cement plant equipments. The bench- and pilot-scale experimental studies indicated that the obtained sulfoaluminate cement product had excellent performance. FACTSAGE was improved by a new database and then used for raw material proportion optimization. The mineral phases of a CaO-SiO2-Al2O3-CaSa(4) system after calcination were calculated. The theoretical and experimental results are accordant. This technology has good potential to decrease the raw material costs and energy consumption at cement plants. It is also beneficial in CO2 emission reduction and circular economy development. The calculation results may be generally referred in the studies on the chemical processes such as sulfur fixation at high temperature, mineral optimization, and cement production, etc.