It is attempted to make an advanced model for the flow of water without solid particles in a hollow-fiber membrane module for plasma separation including the tubular shell part, considering that part is similar to a packed column. On the basis of the model, distribution of pressure and flow rate in hollow-fibers and in the tubular shell are estimated. The availability of the model is confirmed by comparing the estimated distribution with results of measurement of the pressure loss in the shell and that in a hollow-fiber. Furthermore, the probability of reflux is confirmed and the position of reflux is estimated based on the model.