Using crossed experiment method, the influence of casting solutions proportion on the cellulose acetate membrane immobilized acylase was studied, and the properties of the membrane: bubbling point pressure, aperture, porosity and rate of dankness were characterized. The results showed that when the casting solution proportion is optimum, the yield of enzymatic activity can reach 98.2% and enzyme membrane has proper rate of dankness. The residual activity can get 79.7% after it is used repeatedly for 10 times. and after being stored at 4℃ for 60 days almost no out-of-activity is observed.