Abstract: In this paper, the elemental geochemistry method is used to systematically analyze and study the new drilled H4 in Hanjiang Sag, northeastern Pearl River Mouth Basin. Based on the results of elemental geochemistry analysis, the sedimentary paleoenvironment of Hanjiang 15 subsag is analyzed in detail. The Eocene sedimentary environment and its vertical evolution process of Hanjiang 15 Subsag are preliminarily discussed and clarified. The following important achievements and understandings are obtained : ① The evolution history of Eocene water depth, oxidation-reduction conditions, paleoclimate and paleosalinity in Hanjiang 15 Subsag is reconstructed. ② The sedimentary period of Eocene in Hanjiang 15 Subsag is mainly shallow water environment, and the water body is rich in oxygen. However, the water body of the third member of Wenchang Formation is deepened, and the weak oxidation environment is the main environment. ③ The climate of Wenchang Formation was dry during the sedimentary period and changed to humid during Enping period. ④ The Wenchang Formation in Hanjiang 15 subsag was affected by the southeast transgression during the sedimentary period, and the salinity of water increased. However, the sedimentary period of Enping Formation was not affected by the transgression, and the freshwater environment was dominated. ⑤According to the results of element geochemical discrimination, logging facies and lithologic characteristics, the upper member of Wenchang Formation ( near H4 exploration well ) of Eocene in Hanjiang 15 Subsag is mainly shallow water delta deposits. The above research results and understandings have certain guidance and reference significance for deepening the understanding of the Eocene sedimentary environment and the analysis of transgression influence in Hanjiang Subsag.