OBJECTIVE： To set up a method for determination of molecular weight and content of polysaccharide in Bletilla striata. METHODS： HPSEC-ELSD method was adopted. The determination was performed on TSK-GEL G4000 PWXL column with mobile phase consisted of pure water at the flow rate of 0.6 mL/min. The column temperature was 30 ℃， and sample size was 20 μL. Evaporative light scattering detector was used. The molecular weight and content of polysaccharide in 3 batches of B. striata were established. RESULTS： The linear range of weight average molecular weight of B. striata polysaccharide were 24.17-178.00 kD（R2＝0.985 5）. The linear range of BT07 content determination were 0.508 0-5.080 mg/mL（R2＝0.998 4）. The limits of detection and quantitation were 0.116 5 and 0.274 0 mg/mL. RSDs of precision， stability and reproducibility tests were all lower than 2％ （n＝6 or n＝7）. Average recoveries rate were 99.16％-100.20％ （RSD＝0.39％-0.64％，n＝9）. Average retention time of 3 batches of samples was 14.28 min （RSD＝4.35％， n＝3）， and weight average molecular weight was 23.54 kD （RSD＝3.78％，n＝3）. Polydispersity coefficient D，MW/Mn）ranged 1.463-1.578. Average content of sample was 93.4％ （RSD＝4.22％， n＝3）. CONCLUSIONS： HPSEC-ELSD method is simple， rapid， accurate and reliable， which can be used for simultaneous determination of B. striata polysaccharide.