Provided are a novel blue BAM phosphor and a preparation method thereof. In the blue-emitting phosphor, a magnetoplumbite phase is epitaxially formed as a protection film on the β-phase of a blue BAM phosphor. The blue-emitting phosphor has high luminosity and broad color gamut, is invulnerable to mechanical damage, and can create uniform images, and thus, is very useful in fabrication of a high quality plasma display panel.