Abstract: The REY （Rare Earth Element and Yttrium） rich sediments from deep sea is a new potential seabed mineral resource and the REY element occurrence and the significance of provenance indication have become a research hotspot. In this study, we compared two pretreatment methods: sealed acid dissolution and sodium peroxide alkali fusion, for the determination of rare earth elements by inductively coupled plasma mass spectrometry （ICP-MS）.¹¹⁵In and ¹⁸⁵Re were used as internal isotopes to complement matrix effect and correct signal drift. The results of the two methods are consistent with the certified values and the standard deviations of them fall within 6%. Three samples of deep sea REY-rich sediments were pretreated by the two methods, and the REE test results are in good agreement. Therefore, the sealed acid dissolution was proved more suitable for treating a large batch of deep-sea REY-rich sediment samples due to the lower detection limit, smaller matrix effect, and simpler analysis procedure than those of the second method.