Abstract: The diatom ooze sediments were collected for the first time by the Chinese research vessel in 7000m water depth of the Mariana Trench, which is the experimental area of Jiaolong human occupied vehicle. Diatomological analyses show that sediments of about 10cm thickness in the core top are Ethmodiscus rex ooze. The fossil diatoms are dominated by large quantities of the Ehomodiscus rex with fragment status, accompanied by a few tropical open ocean planktonic species, e.g., Azpeitia. The diatom ooze in this deep region genetically indicates that the E. rex bloomed very fast in the geological history, and had important significance for the study of palaeoceanography and micropalaeontology.