Our previous study revealed that drying shrinkage in slag mortar cured at elevated temperatures (40–65 ℃) increases compared to curing at 20 ℃, possibly due to the conversion of ettringite to monosulphate during drying. This study investigates the combined effects of gypsum, limestone powder, and fatty alcohol-based shrinkage-reducing agents (SRAs) on drying shrinkage of slag-based cementitious materials under different curing conditions, focusing on hydration products. X-ray diffraction (XRD) analysis is conducted to monitor the evolution of calcium aluminate hydrates during curing with heating and drying. Results indicate that gypsum and limestone powder stabilize ettringite by preventing its conversion to monosulphate and enhancing slag hydration. Compressive strength was improved by the addition of gypsum and limestone powder, although the effect of SRAs on strength appears to be temperature-sensitive. Drying shrinkage measurements confirm that the additive combinations effectively mitigate shrinkage. Additionally, it was suggested that the effectiveness of shrinkage reduction may be influenced by the molecular structures of SRAs, depending on curing temperature. These findings provide insights into optimizing additive combination to reduce early-age cracking in slag-based systems.