High gradient magnetic separation (HGMS) has witnessed widespread application in many scientific and industrial fields. In this paper, the favorable aspect ratio of matrices in axial HGMS was investigated, providing that matrices' cross-section area were equal. Particle capture models for different circumstances were derived and selection method of applicable particle capture models for specific conditions when varying matrix aspect ratio gamma (1/4 similar to 5) was put forward. Particle capture cross section of matrices under a variety of conditions were depicted and quantified. The horizontal and vertical dimension of the particle capture cross section increases and decreases with the increase of aspect ratio, respectively. The particle capture cross section area increases rapidly and slowly before and after reaching magnetization saturation. There exists a favorable matrix aspect ratio at which the particle capture cross section area (particle capture efficiency) reaches the maximum. The favorable aspect ratio is induction dependent and decreases with the increase of magnetic induction. In scientific studies and industrial practice employing axial HGMS, matrices with the favorable aspect ratio can be adopted basing on results of this investigation, which is quite beneficial for the recovery of fine weakly magnetic particles.