Phosphogypsum based hydraulic cementitious material is a new building material with phosphogypsum of byproduct of phosphating industry as the main raw material.Compared with traditional portland cement and slag cement,phosphogypsum is inactive and cannot be directly used as cementitious material,and must be modified before use.In view of the shortcomings of the current phosphogypsum-based cementitious materials,such as long setting time and low early strength,the effects of material composition and admixture on setting time and early strength were studied to obtain modification method of phosphogypsum based cementitious material.When the mass ratio of slag powder （KF） to silicon-based nano powder（WS） was 3:17 and the mass fractions of sodium silicate（NS）,aluminum rich salt（NA） and high-efficiency polycarboxylate water reducer（JS） were 0.3%,0.7% and 0.3% respectively,the initial setting time could be controlled at 130~260 min and the final setting time could be controlled at 280~600 min.The early flexural strength of mortar was more than 3.5 MPa in 3 d and more than 5 MPa in 7 d.The early compressive strength was more than 20 MPa in 3 d and more than 35 MPa in 7 d.The modified phosphogypsum based cementitious material could replace 25%~40% or more ordinary portland cement in the field of building materials.