Abstract: In this paper,taking the Pueraria lobata roots as raw material,the methods of cellulase auxiliary ultrasound Pueraria lobata polysaccharides and the DPPH free radical scavenging ability of Pueraria lobata polysacharides was also analyzed. On the basis of single factor experiments,three levels of the four factors(cellulose dosage,ultrasonic power,ultrasonic time,ultrasonic temperature)were selected for Box-Benhnken design to optimize the polysaccharide yield rate conditions. The result showed that,cellulase dosage was 6.0%,ultrasonic power was 280 W,ultrasonic time was 52 min,ultrasonic temperature was 65℃,the actual polysaccharide yield rate was 4.93%±0.02%. Compared with the predicted value,the error was within 2%. And the DPPH free radical scavenging capacity of the polysaccharides extracted by enzyme-assisted ultrasonic extraction had IC₅₀ value of 954.97 μg/mL,IC₅₀ value of 1379.60 μg/mL by thermal reflux method,and IC₅₀ value 131.07 μg/mL by V_C. Pueraria polysaccharide had strong activity of scavenging DPPH free radical by cellulase assisted ultrasound extraction. It would provide the basis for the development and utilization of radix Pueraria lobate polysaccharides.