The complex micropore structures of tight sandstone reservoirs leads to an unclear understanding of pore space distribution and flow mechanism. Accordingly，taking the high-temperature，high-pressure，and ultra-low permeability tight sandstone reservoir at Ledong 10 area in Yinggehai Basin as an example，the pore space characteristicss of tight sandstone reservoirs with image analysis techniques such as 3D high-precision micro CT scanning and nano electron microscope scanning were quantitatively characterized in this paper. A two-scale 3D pore structure model based on digital cores was constructed and the flow mechanism of tight sandstone reservoirs based on the two-scale pore coupling flow simulation was determined. The results show as following：①The tight sandstone reservoir at Ledong10 area mainly develops three scale ranges of pores，which are respectively 0.070-3 μm，3-40 μm，and 40-300 μm. ②In the micropore scale dominated by feldspar dissolved pores and rock debris intergranular pores，the difference between pore and throat radius is small. The flow space is composed of micropores and throats，which are characterized by small pores and small throats. The water phase permeability decreases rapidly in the process of gas-water two-phase flow. ③In the two-scale pore structure model composed of large intergranular dissolved pores，mold pores，and secondary scale pores，the flow model presents the characteristics of large pores and small throat，and the water phase permeability decreases slowly.