The results show the per area dendrite number for directionally solidified superalloy DZ417 is increased with a strong static magnetic field at the different drawing speeds and temperature gradient. With enhancing the intensity of magnetic field, the per area dendrite number for directionally solidified superalloy DZ417 gradually increases. This is due to the interactive competition between the magnetic damping and thermoelectromagnetic convection. Therefore, the dendrite number for directionally solidified superalloys can be controlled by tuning the intensity of magnetic field, which may provide a new way for improving the properties of superalloys.