The paper is focused on clarifying the influence of flue gas desulfurization (FGD) gypsum in replacing natural gypsum (NG) in the production of ordinary Portland cement (OPC). FGD gypsum was taken from Yi Yang power plant in Hunan, China. OPC clinker blends with 1–7 % of FGD gypsum to produce the binder of clinker/FGD gypsum. The properties of FGD gypsum was investigated via Chemical analysis, X-ray Diffraction (XRD), and differential thermal analysis (DTA)/thermogravimetric (TG) to evaluate the properties of binder. In present experiment, conduction calorimetry was applied to investigate the early hydration of binders. It was concluded that the blending of FGD gypsum reduced early hydration exothermic peak value of clinker and delayed the appearing time of exothermic peak at 30, and finally the early hydration of clinker was delayed effectively. This FGD gypsum is suitable as cement set retarders.