Abstract: Aiming at tendency of shrinkage cavity and porosity in ZG15Cr2Mo1 reheat main steam valve housing castings caused by large wall-thickness variations and dispersed hot spots, a three-dimensional model of the castings was established, and a horizontal side-gating sand casting scheme was designed based on its structural characteristics, dimensional features, and service requirements. Numerical simulation was carried out to investigate mold filling and solidification behaviors, and the locations and distribution characteristics of shrinkage defects were identified. The casting process was optimized by the combined application of chills and risers. The optimized simulation results show that the shrinkage cavity and shrinkage porosity defects in the castings are effectively suppressed, and the process yield is 75.93%.