The Gleditsia sinensis Lam. seed polysaccharides is a new type of functional polysaccharide with great potential for application in the food industry. In this study， the water extraction and alcohol precipitation method was used to extract the Gleditsia sinensis Lam. seed polysaccharide， and the influence of heterogeneous hygrothermal modification technology on its properties， oligosaccharide preparation efficiency and antioxidant activity was discussed. In this work， polysaccharides was obtained from the seed of Gleditsia Sinensis Lam. with an extraction rate of 17.4%. It was found that the apparent viscosity of the polysaccharide solution (10 g/L) decreased significantly after being modified， from 834 mPa·s to 97 mPa·s； the thermal stability was significantly improved， and the microscopic morphology became smoother and flatter， the particle size was significantly smaller， and the specific surface area increased to 0.245 m2/g. Moreover， the hydrolysis rate of modified polysaccharides (40 g/L) increased by 17.4%， and the content of low molecular weight (<5 ku) oligosaccharides was significantly increased， and the total antioxidant activity was significantly enhanced. These results indicated that the heterogeneous hygrothermal modification technology was beneficial to the preparation of the Gleditsia sinensis Lam. poligosaccharides， and could provide a certain theoretical support for the development and application of the Gleditsia Sinensis Lam.