Abstract: The Jiyang movement was a very important geologic event during the Cenozoic evolution of Jiyang Depression,Bohai Bay Basin.It occurred from the late deposition stage of Sha4 member to early Sha3 of the Eogene.The stratigraphic unconformity between these two members can be observed in a broad area.According to the results of paleontologic analysis,the Daleotopography in this area is characterized by uplifting of highland and deepening of depression,which suggest that the Jiyang movement have a process of block faulting and tilting with large amplitude. The geochemistry of volcanic rocks in Sha4 an d Sha3 member indicates a deep background of enhanced stretching extent of lithosphere,enlarged upwelling amplitude of asthenosphere,intensified of magrrmtism and rising thermal flux during the Jiyang movement,which further suggest an obvious transformation of thermal constitution in lithosphere. Therefore,origin of the Jiyang movement could not be interprated as regional uplifting,and probably is related to deep processes.From the continental geodynamics point of view ,the deformation of crust is the response of deep lithosphere process,and the effective elastic thickness (Te)of lithosphere dynamically controls crust deformation.According to the modem observation of continental geophysics,the accretion of Te could minimize the absolute value of lithosphere deformation and makes the spatial topography variation smooth gradually.Similarly,the decrease of Te could enlarge the absolute value of lithosphere deformation and obviously affect the topography.The mechanism is the change of lithosphere deformation style from elastic to plastic,and the response to sediment load changes from flexural to local isostasy,which is the result of smaller Te caused by transformation of thermal constitution in lithosphere.Hence the variation of Te is an important factor for the paleotopography evolution of basins. After theoretical modeling,this paper confirmed the dynamic origin of Jiyang movement is the decrease of Te,and its amplitude should be larger than 8km ,which caused an altitude difference about 1 000m .The factors causing the decrease of Te include the continuous heating of thermal abnormality in asthenosphere,flowing of the plastic lower crust and displacement of block faulting,etc.