In this study, we address the fundamental problem of magnetic interaction between two magnetite particles in a low-intensity magnetic separator. The accuracy of the magnetic force between two adjacent particles was compared based on the magnetic dipole theories in a 3D model. The results indicate that compared with calculation results of 3D finite element method (FEM), the relative error of the formulas is about 31% when the inter-particle distance ranges from 1.1 to 5 times of the particle diameter. Furthermore, we came up with a more accurate and faster method (formula combined with finite element integration) for calculating the magnetic force throughout the whole range of the inter-particle distance. The results of FEM calculation agreed well with the new method, which can reduce the relative errors of magnetic dipole force to less than 3% in the two magnetite particles system.