Abstract:Bletilla striata （Thunb.） Reiehb.f.was digested with pectinase，based on the single-factor experiment，comprehensive influence of 4 factors contributing to the yield of reducing sugar was inspected：enzyme addition （%），temperature（℃），time（min）and pH.To get the best technologic parameters，optimization model was designed by response surface methodology design.The antioxidant capacity of polysaccharide was studied by the DPPH free radical（DPPH·）method，ABTS free radical（ABTS+·）method and hydroxyl free radical（·OH）method.The in vitro immunostimulatory activities of enzyme hydrolysate were investigated by using the immune activity analysis cell model（RAW264.7 macrophages）.The results indicated that optimized conditions for enzymatic hydrolysis of polysaccharide from Bletilla striata（Thunb.）Reiehb.f.was enzyme addition（1.4%），enzymatic hydrolysis temperature（54.7 ℃），enzymatic hydrolysis time（87.5 min）and pH 5.4.Under these conditions，the extraction rate of polysaccharide from Bletilla striata（Thunb.）Reiehb.f.was 58.32%.Polysaccharide from Bletilla striata （Thunb.）Reiehb.f.have the function of clearing DPPH·，ABTS+· and ·OH exhibited promising antioxidant activity.The research of immunological activity of the polysaccharide showed that it could effectively promote the proliferation of immune cells，and significantly promote the concentration of tumor necrosis factor-α （TNF-α）in RAW 264.7 cells indicated its remarkable immunological activity.