In order to analyze the particularity of diagenetic evolution law of the upper part of 4th member of Shahejie Formation in saline lacustrine basin of Bonan subsag，detailed research on diagenetic environment and evolution law has been carried out with comprehensive application of casting，scan electron microscope and X-ray diffraction data of clay minerals. The result shows that clastic rock，carbonate rock and gypsum salt beds were mainly developed in the upper part of 4th member of Shahejie Formation of Bonan sag. Under the influence of alkali fluid from gypsum and organic acid during early and middle-late stage of diagenetic period，the reservoirs in the study area experienced alkali and acid diagenetic environment in turn. The intensity of early-stage alkali diagenesis affected the occurrence time of acid diagenesis during middlelate stage. The early-stage strong cementation often caused small contact area between organic acid and diffluent mineral in late stage when organic acid entered into reservoir in the middle-late stage. Therefore，the beginning time of extensive dissolution would be delayed. Because of that，the reservoir follows the diagenetic evolution law that reservoirs in middle alkali diagenetic environment at early stage would be dissolved later at middle-late stage；and if they were in weak alkali diagenetic environment at early stage，they would be dissolved earlier at middle-late stage. The alkali-acid alternation of diagenetic environment in saline lacustrine basin caused the particularity in reservoir diagenetic evolution. Under the controlling of this special diagenetic evolution law，the secondary pore developed with large depth in the late time，resulting in a good match between the timing of high quality reservoir formation in deep layers and late hydrocarbon reservoiring.