By using two forms of magnetic field to have an effect on negative corona discharge, the influence of magnetic field on different interelectrode area of corona discharge was studied. The research showed that the charging intensity is changed and the discharge current is increased when the magnetic field is applied to the corona zone. But the discharge current is not changed when the magnetic field is applied to the charging region. This well explained the reasons for the increase of the discharge current. Meanwhile, the research shows that the onset voltage of negative corona discharge is decreased when the magnetic field is applied. The main reason is due to that the electric field intensity of the corona region is enhanced when the magnetic field is applied.