Ultrafiltration has been utilized widely in the dairy industry processes such as the separation and concentration of protein whey solution. In such processes, the critical problem is the decline of permeate flux caused by membrane fouling. Several models have been proposed to explain the behavior of filtrate flux during filtration. Our prior work developed a model which divides the permeation process into two periods according to the dominant factor controlling the filtration resistance. The first period is pore blocking dominant and the second period is cake dominant. In this current work, an improved model is proposed. In the model, it is considered that membrane fouling by pore blockage mechanism and the development of compressible cake layer occur simultaneously. The pore blockage model and compressive yield stress model are modified and coupled to give the numerical prediction of the permeate flux. The calculation results are compared with experimental data of cross-flow ultrafiltration of the protein suspension system. The comparison indicates that entire permeation process is well presented by the proposed combined model. The results contribute a viewpoint for understanding the behavior of membrane and permeate flux in the filtration process. (C) 2012 Elsevier B.V. All rights reserved.