Abstract: The analyses of the major and trace element contents in 45 pieces of core samples from the PC5222 drill hole in the mid-Pacific Ocean has disclosed that vertically, there are marked changes in element contents in different burial depths of sediments. The SiO₂ contents decrease with the increase of the contents of Al₂O₃, Fe₂O₃, K₂O, MnO, TiO₂, CaO and CaCO₃ in the early sediments. The things are different in the late sediments. The element correlation analysis and R-mode factor analysis indicate that there is a markedly positive correlation between the contents of Al₂O₃, Fe₂O₃, K₂O, MnO and TiO₂ while a negative correlation with the SiO₂ contents. The former are influenced by the terrigenous clastic sediments, and the latter by the organic action and volcanic activity.The evolution of the sedimentary environments during the late Oligocene is also explored.