Membrane ultrafiltration of macromolecular solutions is usually analyzed with the gel polarization model, the osmotic pressure model, and the resistance-in-series model. The disadvantages of these conventional models are, respectively, the limited range of application, the mathematical difficulty in treatment and the incorrect definition of the growth of the concentration polarization resistance. In the present work, however, the permeate flux was analyzed with the exponential model, hyperbolic-tangent model, and error-function model. The development of these models is based on three essential ultrafiltration behaviors, and the exponential-function and hyperbolic-tangent models correlate well with the experimental results for polyvinyl alcohol (PVA) aqueous solution.