The invention discloses a cellulose acetate / nano cellulose blended ultrafiltration film, belonging to the technical field of films. The blended ultrafiltration film is characterized by being prepared through the steps of firstly, pretreating raw material filter paper by adopting a water solution of alkali system sodium hydroxide / urea, carrying out suction filtration to be neutral, baking, then carrying out acidolysis by using a sulfuric acid solution, and diluting, centrifuging and drying to obtain nano cellulose; and then by adopting cellulose acetate and nano cellulose as film materials, adding an additive, selecting acetone and N,N-dimethylformamide as a mixed solvent, stirring uniformly, then defoaming, and after film scraping, soaking the material into a gel tank with a certain temperature to obtain the blended ultrafiltration film. The blended ultrafiltration film has the effects and benefits that the obtained ultrafiltration film has the good performances of cellulose acetate / nano cellulose, the porosity of the cellulose acetate / nano cellulose ultrafiltration film is improved, the pore diameter is increased, the hydrophilicity is improved, the ultrafiltration film has the advantages of high flux, good pollution resistance, good mechanical performance and the like, the operation is simple, the pretreatment is not needed, and the cost is low.