A lightweight water-soluble core mold material for hollow shell composites was prepared by hot drying process with polyvinylpyrrolidone (PVP) aqueous solution as the adhesive and hollow glass microspheres as the matrix material. The effects of the content of adhesive and different treatment methods on the flexural strength, compressive strength and dissolution rate of the core mold were studied, and the microstructure of the core mold material was observed by scanning electron microscope. The results show that adhesive dosage of 40%, the flexural strength and compressive strength could reach up to 3.346 MPa and 3.499 MPa, with a water solubilization rate of 0.238 g/s. After the coupling agent treatment and high temperature treatment, the core mold strength and dissolution rate are improved, and the modification effect is good; small filler sizes can effectively fill the gap formed by matrix materials accumulation, improve the mechanical strength and affect the water solubility rate. The properties of water-soluble core can meet the requirements of resin transfer molding (RTM) and vacuum bag molding, which provides a solution for the integrated molding of profiled hollow profiles.