Investment casting is a precision casting method that enables the casting of difficult-to-cast and high-melting-point materials with excellent surface quality. Mold temperature is a crucial parameter that significantly impacts product quality, energy consumption, and the overall production cycle. This study investigates the impact of mold temperature on shrinkage and shrinkage porosity in SUS304 stainless steel using simulations and experiments supported by Magma software. The research results show that the experimental results are in complete agreement with the simulation results. Through this study, the effect of temperature on shrinkage has been evaluated, and the mechanism of defect formation has been explained. Mold temperature has a significant influence on casting defects and properties. Higher temperatures reduce the shrinkage and porosity of casting, with a higher 900 °C yielding the best microstructure. While higher mold temperatures generally decrease shrinkage, the extent of this decrease varies with the dimensions. Ultimately, simulation and experimentation are invaluable tools for streamlining production, reducing costs, and improving product quality.