This study was analyzed the structure and characteristics of soy hull polysaccharide by ammonium sulfate graded， which used by molecular weight， monosaccharide composition， Fourier transform infrared spectroscopy(FT-IR)， scanning electron microscope (SEM)， atomic force microscope (AFM)， thermogravimetric analysis (TG) and rheological analysis. The study found that the water-extracted soy hull crude polysaccharide (WSHP) was mainly composed of galactose and mannose， while the polysaccharide fraction graded by 40% and 60% ammonium sulfate (ASHP40， ASHP60) was mainly composed of galactose and xylose. In addition， ASHP40 had the highest polysaccharide content， reaching 55.67%， and its relative molecular weight was lower than WSHP. The surface structure of ASHP40 and ASHP60 was loose， and ASHP60 had an obvious network structure. However， ammonium sulfate grading reduces the intermolecular interactions of polysaccharide components， resulting in low apparent viscosity and poor thermal stability. Therefore， this study proved that soy hull polysaccharides graded with ammonium sulfate had different compositions and microstructures， making these thermal stability and rheological properties significantly different.