Many high-end industrial castings can't be machined due to its complex structure or narrow gap, which need sand cores to be auxiliary forming during casting. Traditional core materials consist of sand and binder or clay. Due to the high-temperature thermal impact of molten flows, the sand core eventually forms hard and brittle tissue that cannot be removed. The decomposition of brittle core needs through high-temperature alkaline cooking for a long time. This process is time-consuming, increasing staffing costs and causing environmental pollution. Therefore, the purpose of this research is to develop a water-soluble cores (WSCs) material formula and manufacturing technology. In addition to the structure capable of withstanding the high thermal impact of molten iron, the sand core inside the casting can be removed by rinsing or soaking in the water jet.