Abstract: Firstly, the effects of operation pressure, temperature and pH value on the ultra-filtration of polysaccharide from Stachys floridana Schuttl. ex Benth (SFPS) were investigated. Then, a multi-factor orthogonal experiment design was conducted to optimize the conditions of ultra-filtration based on the results of the single factor experiment. Finally, the optimal method for cleaning the membrane was determined by evaluating the membrane flux of water before and after the clean of membrane. As results, it was determined that ultra-filtration was better than conventional method for the concentration of SFPS, and the optimal conditions were determined as following: operation pressure 0.35 Mp, temperature 30 ℃, and pH value 6.5. The suitable method for the clean of membrane was washing the membrane with pH 8.5 NaOH solution at 40 ℃ for 0.5 h.