Fourteen rare earth impurities in high purity yttrium oxide were determined by series triple quadrupole inductively coupled plasma mass spectrometry（ICP-MS/MS）.Under the best working conditions,the analytical mode of the sample was determined as the mode of TQ-He.The effect of He and O₂ as reaction gases on the detection limit and the equivalent background concentration（BEC） was investigated,which could eliminate the interference of polyatomic ions that produced by yttrium oxide matrix more effectively.The interference of collision mode could be eliminated to achieve the purpose of accurate determination of trace rare earth impurities in high purity yttrium.In the helium mode,the detection limit of rare earth elements was between 0.007 μg/L and 0.89 μg/L in experiment.The recovery was 97.93%~104.86% and the relative standard deviation was 0.78%~3.39%.The method had the advantages of simplicity and high precision,which could meet the direct determination of 14 rare earth impurity elements in high purity yttrium oxide with a purity of 99.999%~99.999 9% and above.