The northwestern coast of the Bohai Bay is the most active in the North China Plain.The study of Quaternary strata can provide the background data for regional seismic geology and hydrogeology.Based on the lithology,structure,and sporopollen analysis of sediments in QHJ01 hole,along with the results of paleomagnetic dating,the climate and sedimentary environment evolution process since 5.20 Ma was reconstructed.QHJ01 hole reveals that during the early stage of 5.20~3.33Ma,the vegetation type was mixed forest of broad leaved trees and some coniferous trees,suggesting a warm and wet climate.During the late stage of 5.20~3.33Ma,the vegetation type was mixed forest of coniferous trees and broad leaved trees,indicating a cool and dry climate with a sedimentary setting of lake.During the period of 3.33~ 2.12Ma,the vegetation type was dominated by desert steppe,with some areas being mixed steppe and broad leaved trees,suggesting a cool and wet climate and a sedimentary setting of meandering stream and floodplain,with the latter less affected by the former.2.12~1.78Ma was the period of lake development in which vegetation type was mixed forest of coniferous trees and broad leaved trees,indicating a cool and wet climate.1.78~0.90Ma witnessed a dry and cool climate and 0.90~0.13Ma a variable climate,during the periods the sedimentary environment was less affected by climate but controlled by regional tectonic subsidence.Since the period of 0.31Ma,the climate fluctuated distinctly,getting warm with increasing of broad leaved contents.The early sedimentary environment was dominantly alternative development of lake,lake delta and floodplain,and the late environment was mainly marine delta.The sedimentary environment was affected distinctly by climate change and also controlly by regional tectonic subsidence since 0.13Ma.