The waste CaSO4 from desulfurized gypsum is used as resource to prepare calcium-based oxygen carrier for chemical looping combustion, which has the characteristics of easy access to raw materials, low cost and high oxygen loading rate. The desulfurized slag was used as raw material, CaSO4-CuO, CaSO4-Fe2O3 and CaSO4-CuFe2O4 mixed oxygen carriers were prepared according to the template-sol-gel combustion synthesis method adopted by the research group. Five reduction and oxidation cycles of the four oxygen carriers and coal were carried out in a high temperature fixed bed reactor. Discovery of the reaction mechanism and sulfur release rule of coal chemical chain were studied in detail. The results show that the mixed oxygen carriers of desulfurized slag-CuO reaction activity is obviously improved, and the loaded CuO reduces the release of sulfur-containing gas. Desulfurized slag-Fe2O3 improves the reaction activity of the oxygen carrier. Desulfurized slag-CuFe2O4 mixed oxygen carriers increases the carbon conversion efficiency, has good reaction activity and circulation characteristics, and it is completely feasible to be used in coal chemical looping combustion. The activity of oxygen carrier of desulfurized slag mixed with Cu and Fe increases obviously, but the mixed oxygen carrier has partially sintered and deactivated during multiple cycles. In the side reaction of desulfurization slag mixed oxygen carrier and coal, Cu and Fe show good sulfur fixation effect, in the side reaction of desulfurized slag-CuFe2O4 mixed oxygen carrier and coal, the peak concentration of SO2 gas is only 37×10-6.