<p>Magnetic filters are widely applied in subway air purification, yet existing research predominantly focuses on cylindrical magnets and lacks simple empirical formulas to describe filtration efficiency and resistance. In this paper, a magnetic filter model with elliptic magnets is established. Based on this model, a two-dimensional simulation was performed. The factors affecting the filtration efficiency and the filtration resistance are investigated: magnet shape factor, inlet airflow velocity, magnetic field strength, blockage rate and particle diameter. Among them, the filtration efficiency of the magnetic filter increases first and then decreases with the increase of the magnet shape factor, and the resistance decreases first and then increases with the increase of the magnet shape factor, that is, there exists an optimal shape factor respectively, which can maximize the filtration efficiency or minimize the resistance. The best shape factor is influenced by other factors. Finally, the empirical formulas of the filter efficiency, filter resistance, the best shape factor are given, which can be used to select the magnet shape, calculate the filter efficiency and filter resistance in practical magnetic filter design, and has a certain guiding role in the manufacture and optimization of magnetic filters.</p>