A lightweight and high-strength water-soluble core mold for composites was prepared by hot-air drying method using aqueous solution of polyvinylpyrrolidone as the adhesive and hollow glass beads, gypsum and graphite as the matrix materials. The effects of adhesive content and matrix material on the mechanical properties and dissolution rates of the water-soluble core mold were investigated. The effect of modification methods on the mechanical properties of water-soluble core molds was investigated, and the microscopic morphology of the modified water-soluble core mold was observed by scanning electron microscopy (SEM), and its modification mechanism was initially explored. The results shows that the density of water-soluble core mold is 0.46~0.58 g/cm³, and the high-temperature treatment and the compounding of glass beads with different scales of particle size are the effective means of modification. The flexural strength of the water-soluble core can reach 7.46 MPa, the compression strength reaches 7.45 MPa, and the dissolution rate is 1.11 g/min before the modification, while the flexural strength of the modified core mold can reach 13.21 MPa, the compression strength reaches 13.45 MPa, and the dissolution rate is 6.34 g/min. The comprehensive performance of the water-soluble core mold can meet the requirements of the composite molding process, and it provides a solution for the integrated molding of the hollow profiled composites.