A simple semi-theoretical steady-state model for the convective flux in cross-flow microfiltration has been developed based on the mass balance. The model, which has two coefficients, A and K, can describes the cake increase on membrane surfaces in a hollow-fiber membrane module and predicts its membrane flux decline. Then this model was validated by using yeast suspensions in a 0.1 mu m hydrophilic polyvinylidene fluoride (PVDF) hollow-fiber membrane module with a 0.3 m(2) filtration area. The experimental and analysis results showed that the two coefficients, A and K, actually varied in a small range, but when the overall average values of A and K were taken into the model as two constants under the different operating conditions, the experimental observation is in good accordance with the model prediction and the absolute value of relative error is less than 7%. So it was advisable to consider the model coefficients, A and K, as two constants in the model to predict the steady-state flux decline in industrial applications.