Objectives: Jimsar shale oil in Junggar basin is a typical continental shale oil in China. The main purpose of this paper is to study the microscopic occurrence characteristics and genetic mechanism of shale oil in sweet spot reservoir of the Lucaogou Formation in Jimusaer Sag. Methods:The occurrence characteristics of shale oil in micro-nano pores were studied by FESEM, LSCM, nano CT, NMR and other experimental techniques.  Results: the sweet spot reservoir has a full scale oil bearing characteristics of nanometer-submicron-micron. At the micro-nano scale, oil and water occured in the form of heavy oil attached to the wall of the pore above 2~5 μm and filled in the pore below 2~5 μm. The intermediate oil occured in the center of the pore above 2~5 μm, and Pore water content is small, isolated in the center of the pore above 2~5 μm, and is encased by intermediate oil.  Conclusions:The occurrence of shale oil in micro-nano pores is not only controlled by hydrocarbon generation overpressure charging, but also affected by adsorption and multi-stage accumulation. The main reason for hydrocarbon adsorption is the change of pore surface wettability from hydrophilic wettability to lipophilic wettability. The multi-stage accumulation results in the difference of oil quality and high oil saturation in nano-micro pores. The heavy component oil injected into the reservoir by hydrocarbon generation overpressure in the early stage and adsorbs on the pore surface under the oil-wetting condition. As the adsorption layer thickens, the nanoscale pores are gradually filled and the pore water is displaced to the middle of the larger pores. Later mature intermediate component oils are further charged and adjusted in this manner. The research shows that the western part of the depression with large buried depth is the favorable exploration direction. The heavy component oil in the micro-nano pore is the direction of shale oil EOR in the future.