In this work, the optimization of the geometry and the electronic properties of the host matrix KMgBO3 were investigated using density functional theory, and the comprehensive photoluminescence and chromaticity properties on five rare earth ion-doped (RE = Ce3+, Tm3+, Tb3+, Eu3+, Dy3+) KMgBO3 phosphors were also studied. By introducing RE ions into the KMgBO3 host, excellent purple, blue, green, red and white emitting light could be obtained under the near-ultraviolet light excitation. The results suggest that rare earth doped KMgBO3 phosphors are potential luminescence materials for the application in the near-ultraviolet white light-emitting diodes.