The influence of magnetic field on corona onset voltage was studied in the earthed atomizing corona discharge, and the charging mechanism was studied in earthed atomizing corona discharge under magnetic field. Eventually, the charging mechanism of earthed atomizing discharges under magnetic field was analyzed. The results show that the corona onset voltage of the earthed atomizing corona discharge is decreased because the magnetic field is used, and the charging efficiencies is enhanced by magnetic field. But the influence on the diameter of water drops was not obvious. In addition, the minimum values of discharge currents are exist in the earthed atomizing corona discharge when the magnetic field is used or not.