The ultrasonic-assisted extraction technology of crude polysaccharide from Achyranthes bidentata Blume and its antioxidant activities of the polysaccharide were investigated.On the basis of single factor test,extraction technology condition was optimized by orthogonal test.Our results showed the best extracting condition was as follows: ultrasonic power 1 000W,extracting temperature 60℃,extracting time 60 min,and material-water ratio 1∶ 30.Under the above conditions,the extraction rate of the crude polysaccharide can reach to 6.1%.Meanwhile,the scavenging activity of the polysaccharide on H2O2,O-2 · and ·OH free radicals were both significant.The clearance rates was up to 75.1%,90.3% and 61.3% respectively.