Effect and mechanism of activation of activator to fluorgypsum, strength, softening coefficient and leaching toxicity of composite cementitious material are studied. Through activation testing of NaOH, Na2SO4 and NaF, the optimum adding quantity was defined as 1%. On the basis of it, 80% fluorgypsum was further processed to improve its quality with slag, fly ash and clinker. With 1% Na2SO4, 25% slag, 5% fly ash and 89% fluorgypsum, the cementitious material properties were excellent; the 28-day compressive strength could reach 12.25 MPa; the softening coefficient was 0.70; and the concentration of fluoride could be reduced to 0.7485 mg/L. The analysis of SEM and XRD show that gypsum, a few calcium silicate hydrate, ettringite and calcium fluoride are filled and packed each other, which hampers water enter particle structures, increases the water resistance of cementitious material and reduces leaching toxicity of cementitious material.