In this project, the complete design process of the plastic injection mold for the cartridge shell of lever valves was carried out in an integrated manner, from the 3D modeling stage of the part and mold assembly in SolidWorks to the analysis of the injection process in Autodesk Moldflow Insight. In the design section, all mold components, including the gate system, gate, runner, ejector mechanism, cooling system, and standard mold parts, were designed and assembled with the aim of achieving accurate performance and high manufacturability. Then, by performing injection simulation, parameters such as filling time, melt flow pattern, temperature distribution, cooling system performance, the possibility of weld lines, air entrapment, shrinkage, and part warping were examined. The results of these analyses allowed for the optimization of the mold design before manufacturing and, by reducing trial and error, led to improved part quality, reduced production cycle time, increased mold life, and reduced mass production costs.