Cinnamon essential oil has gained widespread attention in the food industry as a safe and effective preservative. However, its low water solubility and high volatility limit its application in food, making the use of natural emulsifiers for its emulsification an increasingly popular focus of research. This study focuses on the extraction of galactomannan-rich aqueous extracts from Gleditsia sinensis seeds using a low-energy, low-pollution microwave-assisted method. The extracted aqueous extracts from Gleditsia sinensis seeds was combined with soy protein isolate to prepare a cinnamon essential oil emulsion, followed by physicochemical characterization and stabilization mechanism studies. The emulsions demonstrated excellent storage stability at 4 °C, along with robust ionic, pH, temperature, and freeze-thaw stability. Furthermore, the emulsions exhibited significant antioxidant activity and effectively inhibited the growth of Staphylococcus aureus and Listeria monocytogenes, highlighting their potential for application in food preservation. Preservation trials with orange juice confirmed that our emulsion achieved preservation comparable to that of the commercial food preservative potassium sorbate. These findings provide valuable insights for developing stable and functional natural food emulsifiers.