In computer-assisted surgery (CAS), the surgical instruments in patient need to locate. To avoid the line of sight (LOS) problem in the optical tracking (OPT), magnetic tracking (MT) technology is usually adopted. A new multi- dipole model of cylindrical magnets, which can avoid limited tracking range and lower tracking accuracy problems that appear in signal magnetic dipole model of cylindrical permanent magnet, is proposed. This model approximates cylindrical magnetic dipole as multiple dipoles ranging along the magnet′s axis, and tracking results are obtained through adaptive particle swarm optimization (APSO). Compared with classical method, the proposed model can ensure its validity in near magnets region. Experiments show that, the solution can decrease positioning error by 15.5%~31.6%, and decrease orientation error by 10.5%~24.4%.