Abstract: Changes in palaeoenvironment and palaeovegetation, and implications for climatic fluctuations were discussed in this paper, based on micropaleontological fossils including spores, pollen, freshwater algae and dinoflagellates cysts from the Well WZ5-X-Y which is located in the Weixinan Depression of Beibuwan Basin. Results suggest that the study area was a palaeolake during the study period. The lake shrank in Neogene but invaded by sea water in Miocene. The Paleogene vegetation was dominated by evergreen deciduous broadleaved forest, indicating a warm and humid climate condition, while the expansion of coniferous forest and contraction of evergreen broadleaved forest during Neogene suggest the decline of the temperature and humidity. The relatively wide distribution of evergreen broadleaved forest during Miocene indicate the improvement of the climate conditions.