Orthogonal experiment was carried out to study the influence of polymer and mineral additives on the strength, water resistance, adhesion and setting property of calcined gypsum modified by composite admixture. The morphology and distribution of the hydraulic materials of the hydrated gypsum were analyzed by scanning electron microscope, X ray diffraction and pore structure testing. The results show that the composite admixture made of the polymer 5010, white cement and fume can improve the strength, adhesion and water resistance of calcined gypsum. The composite admixture not only decreases the size of the crystalline phase particles, but also increases the amorphous phase content and improves the compactness of hardened paste.