Abstract: To investigate the effect of Ca²⁺ on the structural and functional properties of starch in the mung bean composite system, mung beans were subjected to various soaking treatments. The structural characteristics of the mung beans were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and infrared spectroscopy (FT-IR), among other techniques. The functional properties of mung bean starch were evaluated through hydration characteristics, thermal properties, and gelatinization behavior. Additionally, the antioxidant capacity of the mung beans was assessed based on their DPPH and ABTS⁺ free radical scavenging abilities, and the in vitro digestibility of the starch was systematically analyzed. The results demonstrated that ultrasonic-assisted CaCl₂ treatment exhibited the most significant impact on the structural and functional properties of mung bean starch and mung bean, compared to individual ultrasonic treatment or CaCl₂ soaking alone. Specifically, the relative crystallinity of mung bean starch decreased by 7.87%, and irregular block-like and clustered aggregates formed between starch particles. The orderliness of the starch decreased by 0.12, and the double helix degree declined by 0.15. Furthermore, the water absorption index increased by 2.73, the swelling capacity rose by 1.94, the initial gelatinization temperature increased by 26.86 ℃, and the enthalpy value decreased by 1.05 J/g. In terms of antioxidant activity, the DPPH radical scavenging ability improved by 12.18%, and the ABTS⁺ radical scavenging ability increased by 14.2%. Additionally, the hydrolysis rate of mung bean starch decreased by 10.02%. This study provides a theoretical foundation for the development of mung bean-based foods with low glycemic index (GI) and high-antioxidant properties.