A high-brightness yellow-orange yellow phosphor for use in warm white LED (light emitting diode), the high-brightness yellow-orange yellow phosphor comprises a substrate based on a rare-earth garnet and cerium for activating said substrate. The high-brightness yellow-orange yellow phosphor has the substances of Li+1, Mg+2 and N−3 contained therein so that the overall stoichiometric equation of the substrate is: Σ(Ln)3Al5−xLi(x+y)Mg(x+y)O12−3yN3y and, the high-brightness yellow-orange yellow phosphor radiates in a visible orange yellow band at λ=538˜569 nm when activated by a shortwave light from an InGaN semiconductor heterostructure.