Abstract: The pilot scale test was carried out on the technical feasibility of polysaccharide recovery from sweet potato starch processing wastewater by combined process of ultrafiltration( UF) and nanofiltration( NF),concretely,the influence factors including operating pressure,influent flow,operating time on NF membrane separation effect were investigated and the cleaning parameters of NF membrane was optimized by orthogonal experiment. The UF membrane( 60 ku) was used as pretreatment and the removal ratio of protein was 94.1% with operating pressure of 0.2 MPa,influent flow of 550 L / h. The concentration of polysaccharide in NF membrane permeate was 4.8 mg / L as well as the rejection rate of polysaccharide and COD highly reached 98% and 85.2%respectively with operating pressure of 0.3 MPa,influent flow of 450 L / h,operation time of 3 h. Orthogonal experiment indicated that the cleaning time,the kind and concentration of cleaning agent would lead to an enhanced recovery rate of NF membrane flux( p < 0.01),however,the cleaning temperature had no significant effect( p > 0.05). According to significant degree of cleaning parameters impacted on recovery of NF membrane flux,it was sorted by cleaning time > kind of cleaning agent > concentration of cleaning agent > cleaning temperature.The recovery rate of NF membrane flux reached 92.1% under optimum conditions that the alkaline protease concentration was 0.06%,cleaning time was 15 min and the cleaning temperature was 30 ℃.