The Paleogene Shahejie Formation in Liaodong Gulf area is rich in oil and gas resources，which is an important target for exploration and development of middle-to-deep hydrocarbon reservoirs. J Oilfield is a typical middle-to-deep hydrocarbon reservoirs in Liaodong Gulf. The calcareous sandstone was drilled by development wells there，which affected the quality of reservoirs and restricted the effect of oil field development. Based on the core，thin section，SEM，drilling and logging data，the characteristics and genetic mechanism of calcareous sandstone and its controlling factors of the second member of Shahejie Formation in J oilfield were discussed. The results show that the formation and distribution of calcareous sandstone are affected by both sedimentation and diagenesis. The calcareous sandstone is characterized by fine granularity，low oil saturation，poor physical property and high density，which is resulted from the diagenesis of shale at the top and bottom of the sandstone. Affected by the sedimentation，the type and vertical position of carbonate cementation are controlled by the sediment thickness and rhythm of sandstone，while the sedimentary facies and mudstone thickness affect the horizontal distribution and cementation degree of the calcareous sandstone. Based on the horizontal distribution characteristics of the mudstone in the first member and the sandstone in the second member of Shahejie Formation，the horizontal distribution of the calcareous sandstone in the second member of Shahejie Formation was predicted. The center of the basin，characterized by thin sandstone and thick mudstone，is the favorable development area of calcareous sandstone and its development degree controls the quality of reservoirs.