Abstract: The effect of solubiliy parameter of 12^# types of organic solvent on the water content of CA ultrafiltration (UF) membranes was studied. It is found that if DMF, with large solubility parameter and strong hydrophilous action with water, is used, the pore size of UF membrane is large; if CA-DMF-Licl system is used, the UF membrane, the MWCO of which is 156000, was obtained. The influential factors of membrane performances were studied in detail, and the rejection, f=93-98%, water flux J=96-120 (mL/cm²·h) at the operating pressure of 0.05 MPa. When the mixed solvents including acetatic acid, dioxane mixed with acetone respectively were used, the UF membrane, the MWGO of which is 35000, was obtained.