The electrostatic cyclone precipitator (ECP) has been widely utilized in industry to control particle escape. However, the dust-removal performance of submicron particles which are the most difficult to be collected in traditional purification technologies cannot meet increasingly strict environmental standards. In this work, the cyclone precipitator was improved through changing vortex, a coupling theoretical model was built, and the dust-removal performance of submicron particles in an improved ECP under different flue gas velocities and magnetic induction intensities was investigated. It is found that compared to cyclone precipitator, the dust-removal efficiency in an improved ECP is significantly promoted with a maximum increase of 52.7%. At the submicron scale, as the particle size increases, the dust-removal performance of the improved ECP declines. The collection performance of submicron particles with or without the magnetic field gradually increase with the drop of the flue gas velocity. The improved range of dust-removal efficiency caused by magnetic confinement effect can reach 7.7% - 10.8%. At the same time, the higher the flue gas velocity, the greater the enhancement of the dust-removal efficiency caused by magnetic field. The results can provide new ideas for ECP structural improvement and insights into the profound removal of submicron particles caused by the combustion of fossil fuel.