The sand casting process of 18CrNiMo7-6 gate valve casting was designed in this paper. The molding and core making methods of castings are sodium silicate CO₂ method and self hardening cold box method respectively. The technological parameters of the casting were determined. The middle pouring system and top riser were designed. Using software to draw the assembly and 3D entity of gate valve casting. ProCAST simulation software is used to realize the numerical simulation task of the gate valve casting process. Shrinkage and porosity are the main research objects. It is found that the defects mainly appear in the thick part of the casting and the flange through the simulation experiment feedback parameters. In this paper, from the point of view of reducing and avoiding defects, the casting process is improved and improved. Finally, according to the experimental results, S2 (with chill) is determined as the final scheme.