An unsteady-state model for cross-flow microfiltration of lactic acid fermentation broth is presented in this manuscript. Compared with earlier models, the improved model can calculate specific cake resistance and membrane fouling resistance simultaneously. Filtration properties are obtained by solving the model with numerical integration and optimization. The model has been used for the analysis of experimental data and the results show good agreement with the experimental permeate flux. The model predicts smaller specific cake resistance by taking into account the membrane fouling resistance.