This standard specifies the determination method of fifteen rare earth element oxides in the mixed rare earth oxides of ionic rare earth ores, which is suitable for samples with TREO (total rare earth oxides) content ≥ 80%. The determination range covers 0.20% to 99.00% of the mass fraction of rare earth element oxides. Methods The accurate matching components of each rare earth element oxide were determined by X-Rays Fluorscence analysis technology, combined with the strength ratio of the characteristic line and the mathematical model.