Abstract: Mechanical entrainment, magnetic entrainment and competitive capture occur in the separation process of high gradient magnetic separation, ultimately leading to a number of problems such as poor selectivity, clogging of the sorting chamber and low sorting efficiency. At present, the theoretical study of high gradient magnetic separation mainly focuses on particle force analysis and calculation, the construction of particle trajectory model and particle stacking model, and the research and development and optimisation of polymagnetic media. Based on the particle force, this paper analyses the causes of poor selectivity as well as low efficiency through the particle stacking model and trajectory model, and reviews the development and optimization of matrix, aiming to provide a reference for the optimization and theoretical research of high-gradient magnetic separation technology in industrial applications, as well as looking forward to the future trend of theoretical research of high-gradient magnetic separation technology.