The optimum condition of ultrasonic extraction of Polygala tenuifolia Willd. Polysaccharide (PTP) was investigated. The results showed, the optimum condition was ultrasonic extraction time 30 min, ultrasonic extraction, temperature 67 ℃, ratio of water to raw material 101（mL/g）, and extraction 2 times, the yield of polysaccharide was（5.87±0.21）% (n=3). IR spectra predicted PTP had typical characteristic absorption peaks which were neutral polysaccharide and free from urinic acid. In vitro antioxidant activities showed PTP had effects on DPPH radical and hydroxyl radical.The IC₅₀ of it against DPPH radical and hydroxyl radical was 0.83 mg/mL, 1.29 mg/mL.