A kind of FGD gypsum from Ningbo Beilun Power Plant of China and fly ash were used as the raw materials with which a complex cementing material was made. Effect of the related factors such as paste material, water proportion, mineral admixtures (Cement, CaO) and chemical activators (NaOH, CaCl2, Na2SiO3, K2SO4) on characteristics of FGD gypsum-fly ash complex cementing material (noted as FGD-GFCM) is studied through a large number of single factor experiments. The additives with significant effect were chosen and the optimal mix proportion was determined. The experimental results show that an appropriate amount of admixtures can effectively improve the strength of the FGD gypsum–fly ash complex cementing material presented here. It is concluded that the strength of FGD-GFCB for 28d is best as the ratio of gypsum and fly ash is between 2:3 and 1:1 and water aggregate proportion is inversely proportional to the cementing material strength and apparent density of it.