Abstract：The mechanical properties and microstructure of flue gas desulfurization gypsum doped with aluminate cement (AC) and ordinary Portland cement (OPC) are investigated. Results show that the initial and final setting time are prolonged to 54.5min and 64min respectively, the flexural strength and compressive strength are increased up to 15.3MPa and 43.6MPa respectively doped with AC. And the initial and final setting time are only 4min and 5.5min respectively, the flexural strength and compressive strength are increased up to 14.3MPa and 36.3MPa respectively doped with OPC. The setting time, flexural strength and compressive strength are ranged between single doped when these two kinds of cement are doped at the same time. The ettringite (AFt) and C-S-H gel are observed in all samples. Filling the role of AFt and cementation of C-S-H gel are the reason for the composite cementitious material reinforced.