In order to clarify the influence of original sedimentary components and water environment on diagenetic evolution of clastic reservoirs，the 3rd member of Shahejie Formation of Paleogene in Bonan Sag，Jiyang Depression was analyzed with drilling，logging and a large number of testing data in detail. The results show that the lowstand systems tract of the 3rd member of Shahejie Formation in Bonan Sag is in a near-subaqueous and brackish water sedimentary environment. The clastic reservoir is rich in carbonate rock debris and has low resistance to compaction. In addition，the brackish water environment makes it undergo strong compaction and cementation diagenesis in the early diagenetic stage. The primary porosity of reservoir decreases rapidly and there is not enough space to accommodate organic acids in the middle diagenetic stage.The acid dissolution is weak and the reservoir physical properties are poor at present. The highstand systems tract of the 3rd member of Shahejie Formation in Bonan Sag is a long-distance and freshwater sedimentary environment. Clastic reservoir is dominated by quartz particles and has high resistance to compaction. In addition，the freshwater environment makes it undergo weak compaction and cementation diagenesis in the early diagenetic stage. So the primary porosity of reservoir declines slowly. The reservoir experiences strong acid corrosion in the middle stage of diagenesis and the reservoir physical properties are good at present. The original sedimentary components and water environment are the essential factors leading to the differences in diagenetic evolution of the clastic reservoirs.