China carried out a systematic oceanic survey in the central North Pacific Ocean. The new data show that the total contents of rare earth elements and yttrium (REY) may exceed 2000×10-6 in the central Pacific Basin. Combined with previous data, this study investigated the characteristics and enrichment mechanisms of REY in the deep-sea mud. It has been found that the P and ΣREY displays good correlation. The analysis of various profiles shows that ΣREY varies sensitively to P contents in sediment cores. If the samples with P content lower than 0.25% are ruled out, the ΣREY in deep-sea mud is lower than 400×10-6, indicating that P content has impact on the REY. Given that phosphate in marine environment can inherit seawater negative Ce anomalies and high Y/Ho ratios, all these characteristics of REY-rich deep ocean mud are seemingly related to phosphate precipitation. Our REY leaching experiments show that most P and REY extracted from leacheate has positive relation to ΣREY and P contents. The HCl leacheate is characterized by an obvious negative Ce anomaly, and positive correlations between REY and P, regardless of ΣREY contents. In contrast, ΣREY contents in the insoluble residues are low without negative Ce anomalies. Based on 12 groups of PO43- and ΣREY in the HCl leacheate, it can be estimated that phosphates in the deepsea mud have REY abundances range between 9500×10-6 to 28000×10-6, which is coupled with that in bio-apatite of deep-sea mud. In conclusion, it can be believed that phosphate in deep-sea mud occurs mainly in REE-rich phosphate, and its REE amount is much higher than Fe-Mn oxide’s and aluminosilicate’s. Therefore, change of P contents is vital to REY content and modes in the deep-sea mud. Compared with the REY-poor phosphate formed in the carbonate sedimentary environment, chemical deposition and organic P diagenesis is favorable for the formation of REY-rich phosphate.