A plasma control method for an exhaust gas treating apparatus includes providing an exhaust gas treating apparatus having a plasma discharge space, a coil disposed on an outer circumference of the plasma discharge space, an upper electrode, and a lower electrode; generating plasma in the plasma discharge space; controlling the state of the plasma generated in the plasma discharge space by generating a magnetic field in the plasma discharge space between the upper electrode and the lower electrode; and cooling the reaction tube using a water cooled jacket disposed around the reaction tube. The magnetic field is generated by applying a current to the coil.