Abstract: The reuse of solid waste gypsum and the development of high strength and performance gypsum materials have always been the focus of domestic and foreign scholars. Gypsum-cement-slag composite materials were prepared by adding chemical additives, chemical waste gypsum and calcium sulfate whisker as main raw materials of desulfurization building gypsum, cement and slag. The effects of the content of polycarboxylic acid superplasticizer and citric acid retarder, chemical waste gypsum and calcium sulfate whisker on the mechanical properties of the composites were researched. The results showed that the optimum dosages of polycarboxylic acid superplasticizer and citric acid retarder in gypsum matrix composites are 1.0% and 0.08%, respectively. When the content of calcined chemical waste gypsum is 12%, the 7 d flexural strength and compressive strength of gypsum matrix composites are 3.7 MPa and 12.0 MPa, respectively. The compressive strength is 0.1 MPa higher than that of the control sample. When the calcium sulfate whisker content increases to 3%, the 28 d flexural and compressive strength values of gypsum-based composites with calcined waste gypsum are 8.2 and 31.5 MPa, which are equivalent to the mechanical properties of samples without waste gypsum and calcium sulfate whisker.