Abstract: The solid-solid reaction to generate CaO and SO2 is the dominant reaction between CaS and phosphogypsum. Meanwhile，there are several side effects among the reaction system.Taking into account the actual industrial production，the reaction is carried out in the high-temperature tube furnace with n（CaS）∶n（CaSO4）=1.2∶3，which is based on the mixed atmosphere of N2 and SO2.What′s more， three gases including CO2，CO， and O2 are introduced into the mixed atmosphere gradually to study the influence of atmosphere for the decomposition rate of phosphogypsum. Results show that different atmosphere have different effects on the solid-solid reaction between CaS and CaSO4.A high molar concentration of SO2 and O2 will inhibit the reaction，which significantly reduces the decomposition rate of phosphogypsum.And CO can promote the decomposition of phosphogypsum.But the presence of CO2 has little influence on the reaction. 

Key words: phosphogypsum, mixed atmosphere, inhibition action