In order to improve the poor characteristics of low strength and poor toughness of phosphorus building gypsum, polyvinyl alcohol fibers of different diameters with different content were added to phosphorus building gypsum matrix composites. And the effects of polyvinyl alcohol fibers on the working and mechanical properties of phosphorus building gypsum matrix composites were explored through experimental analysis. The results show that the incorporation of polyvinyl alcohol fiber can significantly reduce the fluidity of the slurry and shorten the setting time of the slurry. At the same time, incorporating polyvinyl alcohol fiber can significantly improve the mechanical strength of the composite when the fiber diameter is 15 μm and the volume content is 16%. In the same composition, the composites mechanical properties are the best, the flexural strength, compressive strength, bending strength and tensile strength are 10071, 1325, 1073 and 289 MPa, respectively. In addition, the microscopic morphology of the material structure was observed by SEM, and it is found that polyvinyl alcohol fiber can be dispersed in the pores and cracks of phosphorus building gypsum, which makes the interior structure of the composite more solid and improves the mechanical properties.