In view of the scale limitations of pore characterization by a single technology and the difficulty in integrating qualitative, structural and quantitative data, the shale in the third member of the Shahejie Formation in the Dongpu Depression, Bohai Bay Basin was taken as the research object, the pore characteristics of the main rock facies (organic-rich massive calcareous shale, organic-containing lamellar clay-feldspar/calcareous mixed shale, and organic-containing lamellar clay shale) were systematically characterized from the micrometer to nanometer scale and from two-dimensional parameters to three-dimensional structures by using multi-scale CT digital core, high-pressure mercury intrusion and low-temperature nitrogen adsorption techniques. Considering that the microscopic pore characteristics at different scales can affect various physical properties of the reservoir, combined with the relative comparison results of rocks, the differences in the microscopic pore characteristics of reservoirs of different lithofacies types were clarified and the factors influencing pore development in this area were explored. The results show as follows. The clay-calcareous mixed shale has the best pore throat connectivity, and the porosity of calcareous shale is the highest. The pore diameters of nitrogen adsorption micro-pores are mainly dominated by those in the range of 3.8 nm to 4.0 nm.. The mercury pressure experiment shows that the meso-macropores are poorly developed due to deep compaction. The pore diameters larger than 3 000 nm in the digital core are mainly concentrated in the range of 1 000 nm to 10 000 nm, among which the throat radius of the clayey-feldspar mixed shale pores is well developed. The pore development of the third member of the Shahejie Formation is influenced by the mineral composition, pore-throat harmony, as well as the type of grain layer and interface characteristics. The results reveal the micro-pore characteristics of different rock phases in the third member of the Shahejie Formation and the influencing factors of pore development, providing a scientific basis for the efficient exploration and development of continental shale oil.