In order to prepare low molecular weight soluble soybean polysaccharide,the process of degrading macromolecular SSPS was investigated by three methods including ultrasonic,hydrogen peroxide oxidation and hydrogen peroxide with ultrasonic treatment.It was found that hydrogen peroxide with ultrasonic treatment had a better effect for preparing low molecular SSPS.The experiments of single factor and orthogonal design for SSPS degradation were subsequently performed.The results showed that,under the fixed ultrasonic power of 100 W,the optimal SSPS degrading conditions were hydrogen peroxide concentration 8%,temperature 70 ℃ and time 1.5 h.Thus the molecular weight of SSPS was degraded from 1.6×105 to 1.09×104.