A light-emitting device with magnetic-source includes a light emitting stack structure. The light emitting stack structure has a first electrode and a second electrode distributed at a light output side of the light emitting stack structure. A magnetic-source layer is engaged with the light emitting stack structure to provide a magnetic field to the light emitting stack structure in a substantially perpendicular direction to the light emitting stack structure. Alternatively, a method for improving light emitting performance of a light-emitting device includes applying a magnetic field to the light-emitting device at a direction substantially perpendicular to a light emitting area of the light-emitting device.