Abstract: The diagenetic densification process of sandstone reservoir is restored and pore evolution law of sandstone in each horizon is established through the study of Chang 6-Chang 9 reservoirs in North Zhifang area of Zhidan Oilfield. The oil charging period and time of Chang 6-Chang 9 oil groups, as well as the accumulation history of oil reservoir in the area, are determined on the basis of analysis on homogenization temperature of fluid inclusions and fluorescence spectrum test. The analysis of coupling relationship between diagenesis-densification-accumulation reveals that the Chang 6-Chang 9 reservoirs are characterized by densification before the hydrocarbon accumulation, which provides a theoretical basis for determination of the main controlling factors of accumulation and prediction of favorable areas in the future.