Abstract: The porosity affect the liquid absorption and ion conduction properties of membrane, thus affecting the performance of lithium-ion battery.As the fiber diameter significantly affect the porosity of membrane,in this research the fiber diameter of electrospun PVDF membrane in lithium cells measured and the test sample designed by the BBD of RSM , a Quadratic multiple regression model got .The R-Squared(0.9466) and Adeq Precision(13.095) illustrated the model fitted the sample very well , small fluctuations between predicted and actual values also said the same result . Under taking analysis of variance and significance test of the model found that acetone mixed ratio, concentration, interaction of mixing ratio and concentration of acetone , interaction of concentration and electric field strength were significant influencing factors .The porosity of the sample Tested by bubble point method and found that fiber diameter of about 100nm in higher porosity and uniform, and as a solution results, obtained a set of optimal parameters: acetone mixed ratio 15.36% , concentration was 18.38%, electric field strength 1.49KV/cm, predicted diameter of 117nm.