Research shows that transitional shales has a small pore volume and poorly developed organic matter pores, leading to lower reservoir quality. However, multi-scale observations reveal organic pores with large pore volume, indicating significant hydrocarbon potential. Further investigation is needed as current studies are insufficient. In addition, due to limitations in the precision of pore structure characterization equipment, the accuracy of quantifying mesopores and macropores are low, leading to an underestimation of gas production in marine-continental transitional shale. Therefore, focusing on the shale of Shanxi-Taiyuan Formation from the Linxing area of the eastern margin of Ordos Basin, by developing method for the higher resolution synchrotron radiation nano-CT at various scales, the large-pore volume and morphology of the shale samples were quantitatively characterized, thereby improving the accuracy and objectivity of large-pore characterization. Besides, scanning electron microscope (SEM), high pressure mercury experiment, nitrogen adsorption and carbon dioxide adsorption experiments were used to characterize the multi-scale pores in transitional shale. Combined with total organic carbon and X-ray diffraction experiments, the pore structure influencing factors were also analyzed. The results show that during the Shanxi-Taiyuan period, shale pore volume is primarily contributed by mesopores (47%) and macropores (45%). The Taiyuan Formation shale has a lower average pore volume of 5.9 × 10^-3 cm³/g. It also features relatively higher clay mineral content and underdeveloped organic matter pores, accompanied by the transformation between clay minerals to form flattened micro-fracture. The total pore volume of the Shanxi Formation shale is 12.5 × 10^-3 cm³/g, with mesopores accounting for 52%. Medium to large organic matter pores are well-developed. Due to the relatively high quartz content and strong compaction resistance, organic matter pores, spherical pores, and intergranular pores with relatively regular shapes are effectively preserved, resulting in favorable reservoir properties. This provides a valuable basis for guiding the exploration and development of transitional shale.