Provided are a method for preparing a blue-emitting BAM phosphor which includes: surface-treating phosphor particles with metal oxide nanoparticles, and a blue-emitting BAM phosphor prepared by the method. The blue-emitting BAM phosphor exhibits better dispersibility and flowability in coating slurry without undergoing a reduction in initial brightness, thereby providing less color variation at ends of a BLU lamp. The blue-emitting BAM phosphor can be directly applied in a currently available method of manufacturing a BLU lamp, and when mixed with existing red and green phosphors, can remarkably reduce color variation at ends of a lamp. Therefore, the quality of a BLU lamp for large-scale displays can be greatly improved.