Abstract: Gypsum mold samples were prepared by put different contents of ceramic-nylon composite fibers into gypsum slurry. The properties and fractures of the ceramic-nylon composite fibers reinforced gypsum mold samples were tested and analyzed. The effect of the composite fiber content on the properties and microscopic appearance of gypsum mold was studied. The results show that the composite fiber content has a significant effect on the properties of gypsum mold. With the increase of the composite fiber content, the flexural strength of gypsum samples has an inverted V-shape, and the flexural strength after calcination does not change much. The gas permeability of gypsum samples increases with the increase of the composite fiber content. When the mass fraction of the composite fiber in the gypsum mixture is 1.25wt%, the gas permeability reaches maximum of 32.3, which is nearly 21 times higher than that of traditional gypsum molds. The pores formed after the roasting of the nylon fiber increase the gas permeability of the gypsum mold, and the ceramic fiber remains in the matrix to increase the strength. When the fiber content exceeds 0.75wt%, the fiber agglomerates and splits the matrix. The thermal conductivity and thermal shock resistance increase first and then decrease with the increase of the composite fiber content. When the fiber content is 0.75wt%-1wt%, the thermal conductivity and thermal shock resistance are relatively optimal.