Abstract: The deep water area of southeast Hainan basin has become one of the most important natural gas exploration areas in the northern continental shelf of the South China Sea. A total of 108 samples were collected from the depth of 3 261.25-5 079.00 m in  Well WN-A for spores and pollen analyses in order to determine the stratigraphic age and reconstruct the paleoclimate conditions. The results show that the fossils are rich in species and distributed continuously, and can be divided into four sporopollen zones including Pinuspollenites-Polypodiaceoisporites-Juglanspollenites-Quercoidites E -Quercoidites D, Pinuspollenites-Juglanspollenites-Polypodiaceoisporites-Dicolpopollis kockelii, Quercoidites E-Polypodiaceoisporites-Pinuspollenites-Polypodiisporites, and Pinuspollenites-Polypodiaceoisporites-Randiapollis reticulatus-Quercoidites E from the bottom to the top of  WN-A well. The sporopollen at 4 425.00-5 079.00 m is dominated by Pinuspollenites, Juglanspollenites and pollen from deciduous Quercus, indicating tropic-subtropical cool conditions, and developing evergreen broadleaved, deciduous broadleaved, and coniferous mixed forest; however, the sporopollen at 3 261.25-4 425.00 m, is dominated by pollen from evergreen Quercus, suggesting tropic-subtropical warm climate conditions，and developing evergreen broadleaved and deciduous broadleaved mixed forest.  This  big climate change from relatively cool to relatively warm is comparable  to the global climate change of Oligocene to Miocene. The depth of recorded climate change, i.e. 4 425.00 m should be the boundary between Oligocene and Miocene.  

Key words: climatic event, spore & pollen, stratigraphy, vegetation, southeast Hainan basin