Abstract: The magnetic focusing Hall thruster, with its strong magnetic field and zero-magnetic-point configuration, has higher requirements for discharge parameters. Loss of stability causes performance to decline and alters the focusing characteristics. In this study, the stability of the magnetic focusing Hall thruster, HEP-100MF, was experimentally and theoretically investigated. The relationship between stability and discharge parameters was experimentally studied, and the reasons for the changes in discharge stability were analyzed based on the experimental results. The process of thruster discharge instability is associated with changes in the electron conduction characteristics, ionization area distribution, and acceleration area distribution.