The concept and method of sequence stratigraphy are used for the study of continental lake basin deposits，and analyses of the environment and sedimentary system have been made in the West Bohai Bay．The Tertiary System in the West Bohai Bay is divided into five sequences，and each sequence is further divided into deposit facies，sedimentary system and system tracts．The sedimentary rhythm of caeh sequence shows the chnage of the level of lake water．The tectonic subsidence and deposition rates account for this change．Thetectonic evolution controls three systems。Every system or system tract consists of several deposit facies types some of which are good reservoir beds