Fluid flow regime and the velocity distribution are effective parameters for systems in which various transport phenomena take place. Besides the properties of the contaminating particles and filter system in the case of high gradient magnetic filtration, the theological properties of the fluid are also important for both design and efficiency of the process. This paper presents a theoretical study about estimation of the velocity distribution in a magnetic filter and the dependence of filter performance on this distribution. A model is presented to estimate the velocity distribution and filter performance in magnetic filtration of Newtonian or weak non-Newtonian liquids. The model is essentially based on the balance of forces acting on particles captured and accumulated in the filter. Model predictions and experimental data given in the literature for Newtonian liquids are in a good agreement.