Simulation of particle motion in the Head Disk Interface (HDI) aids in the understanding of the contamination process on a slider, which is critical for achieving higher areal data densities in hard disk drives. In this paper, the boundary effect—the presence of the slider and the disk—on particle motion in the HDI is investigated. A correction factor to account for this effect is incorporated into the drag force formula for particles in a flow. A contamination criterion is provided to determine when a particle will contaminate a slider. The contamination profile on a specific air bearing surface is obtained, which compares well with experiments.