For the first time this paper studies the sedimentary environment and sequence stratigraphy of Jiyang depression by means of observation and statistics of ostracods occurrence in thin sections.According to the characteristics of ostracods distribution on the level, the distribution patterns of fossil are classified into uniform distribution, dispersed distribution and banded distribution. Based on the ostracods preservation condition, the fossil is classified into double valve, single valve, fracture and flattening deformation. The fossil abundance is sorted into rich (>100 flap/4cm2), medium(30~100flap/4cm2) and rare ( <30 flap/4cm2) . Ostracods occurrence is closely related to the palaeosalinity, lithofacies, sequence stratigraphy and carbonate content of shale . Research shows that: ①The watery environment of Es4cx —Es3x Jiyang depression has undergone an evolution of water body from salty to fresh, where the salinity change is agreement with fossil abundance change. ② The carbonate content in the range of 50%~60% is most conducive to the preservation of ostracods fossil. ③ The fossil abundance of laminated tuffaceous shale facies and laminated argillaceous limestone facies are very high, however, the slow deposition rate during the period of laminated structure formation and firm deposition basement are not favorable to the burial and preservation of ostracods fossil, thus the majority of fossil presence is in form of fracture. ④ The vicissitude of ostracods abundance has a close relationship with stratigraphic sequence. The ostracods abundance sequentially presents three stages：appearance — prosperity — recession，corresponding to the low stand system tract, lake expansion system tract and high stand system tract respectively.This method solving the problem that the primary preservation and the distribution patterns of fossil are difficult to observe using the routine analysis, is able to be used to maximize the fossil information acquisition.