The invention relates to a magnetic-particle particle diameter sorting method. The method includes the following steps that a chromatographic column is filled with a magnetic adsorption medium according to a preset height-diameter ratio to obtain a sorting pipe, the sorting pipe is moved into a magnetic field to enable the magnetic adsorption medium to be magnetized, suspension liquid containing to-be-sorted magnetic particles to be fed, the to-be-sorted magnetic particles are absorbed to the magnetized magnetic adsorption medium, then the sorting pipe is moved out of the magnetic field, an eluant is adopted for elution, and the magnetic particles are collected. By means of the magnetic-particle particle diameter sorting method, the magnetic particles in different particle diameter scope can be sorted, the suspension liquid with the magnetic particles being good in dispersibility, high in stability and narrow in particle diameter distribution scope can be obtained, the sorting process is simple, and efficiency is high.