CO2 emission all over the world is constantly on the rise. In recent years, CO2 capture technology has been improved and innovated. Phosphogypsum (PG) is a solid product of industrial solid waste with an increasing annual accumulation. The research of this paper has carried out thermal decomposition of phosphogypsum under the reduction atmosphere to produce byproduct CaS and mineralization capture of CO2 in a gas-liquid-solid three-phase fluidized bed reactor. Results show that the fluidized bed is more effective and can effectually shorten the reaction time. Meanwhile, different liquid solid (L/S) ratios, temperatures, and pressures have been researched to study the theory of CO2 capture by phosphogypsum. It has been found that the lower the L/S ratio is, the higher the CO2 capture capacity is. At the same time, theoretical calculations show that high temperature promotes the decomposition of CaCO3, thereby inhibiting the capture of CO2, so the whole carbonation process is operated under ambient temperature and pressure. Meanwhile, this paper discusses the calcium migration path and migration mode from the decomposition of PG to the mineralization of CO2, proposes a new idea of CO2 capture, and makes a certain contribution to PG resource utilization.