Abstract: Based on the magnetic field state and fluid velocitydistribution, a dynamic model of paramagnetic particles to be captured byferromagnetic matrix is proposed. The phenomenologicalinterpretation of paramagnetic particle's trajectorydifferent from diamagnetic particle's is valuable on calculating the capture zone.From the observation on coal concentration and de-sulphurization by the High GradientMagnetic Separation (i.e. HGMS), the magnetic field is notaxisymmetrical so that the concept ofcapture radius is not very accurate. According to the Static EquilibriumBuildup Model (i.e. SEBM) proposed by J.E. Nesset and J.A. Finch, the notionof capture zone is proposed, the boundary curve separating thecapture zone and expel zone is found to be a single hyperbolic curve, and thus the newformula for calculating the area of capture zone is obtained.