The binary complex of gallic acid (GA) and mung bean starch (MBS) was prepared by the co-homogenization method. The effects of GA addition ratio on the structural properties, solubility, swelling capacity and hydration properties (such as swelling, aging, rheology, in vitro digestion, and antioxidant properties) of MBS were investigated. The results showed that after being combined with GA, the solubility of MBS significantly increased (P<0.05). When the GA addition amount was less than 15%, the swelling capacity decreased, and adding 20% of GA led to an increase in the swelling capacity. The composite had a lower gelation temperature, gelation enthalpy and rehydration value, and the gel hardness after aging significantly decreased (P<0.05), being easily re-gelated and less prone to aging. The storage modulus (G') and loss modulus (G") decreased, with tanδ < 1, indicating a weak gel system with strong fluidity. When the GA addition amount was 20%, the resistant starch content in the composite significantly increased (P<0.05), and the DPPH scavenging rate increased from 8.31% to 89.03%, and the ABTS scavenging rate increased from 2.12% to 88.30% (P<0.05). The in vitro anti-digestion and antioxidant capabilities were significantly enhanced. The infrared spectrum showed that the short-range orderliness of the composite gradually decreased, and a new peak appeared at 1 695 cm–1. The X-ray diffraction showed that although the crystal type of the composite did not change, the diffraction intensities at 20.0°, 22.0° and 24.0° slightly increased. Both of these indicated that there was an interaction between GA and MBS, mainly in non-covalent forms such as hydrogen bonds. This study provides a reference for the modification of MBS and the application of GA in starch-based functional foods.