Bai Ji is a perennial herbaceous plant Bletilla striata (Thunb.) Reichb. f. of family Orchidaceae, which is also known as Xiao Bai Ji, Lian Ji Cao, etc 1 . Its medicinal part is dried tuber and its medicinal composition is Bletilla striata gum, which contains polysaccharides, starches, glucose, volatile oils, etc. It has less adverse reactions and has lung tonifying, hemostatic, astringent and antibacterial actions 2 , which has all along been used as a traditional Chinese medicine clinically, mainly for the treatment of lung injury, hemoptysis, surgical wounds, ulcers, pyogenic infections, etc. 3,4 . Meanwhile, Bletilla striata gum can also be used as thickeners, emulsifiers and moistouring agents in the petroleum, food, pharmaceutical and cosmetic industries, which has a bright prospect 5 .Bletilla striata polysaccharides are a kind of sticky polysaccharides in the plant obtained by water extraction and ethanol precipitation, their chemical components are glucose and mannose, with a ratio of 1:4, it contents are extremely rich 6 , which account for about 55-60 % of the plant. Therefore, as one important direction for development of novel drugs, biologically active Bletilla striata polysaccharides have gained increasing attention of scholars at home and abroad, in order to find a more reasonable and feasible production process. The present experiment studied the extraction process of total The aim of the study was to optimize the optimal process conditions for extraction of Bletilla striata polysaccharides and its antibacterial activity in vitro. Conventional water extraction and ethanol precipition method with polysaccharide content as an index through single factor investigation and L9(3 4 ) orthogonal table was used to optimize extraction conditions, respectively. The test tube double dilution method was chosen for preliminarily screening of the antibacterial activity and the determination of antibacterial mechanism was according to bacterial state changes in electron microscopy observation. The optimal extraction condition was obtained using cold soaking for 6 h prior to extraction, two times 3 h extraction technology, at 90 °C, with a extract-water ratio of 1:15, for purification using concentration of extract to 1:5 (w/v), addition of a 3-fold volume of 95 % ethanol, ethanol content of up to 80 % and polysaccharide content of 53.72 %, in addition, the MIC to S. aureus was 6.25 mg/mL and MBC could reach 12.50 mg/mL, the mechanism may be related with the permeability of cell membrane. The extraction and purification process for Bletilla striata polysaccharides established in this experiment is simpler, more scientific and suitable and Bletilla striata polysaccharides has a obvious inhibition against S. aureus.