The pore structure of tight sandstone reservoirs is the hot spot of unconventional reservoir geology research. The He 8 Formation in the eastern part of the Ordos Basin is an important reservoir, and further researches are needed to characterize the pore structure of this tight sandstone reservoir. A qualitative study of the pore types and throat types in the reservoir of He 8 Formation was carried out by using analytical methods of ordinary thin section, casting thin section, and scanning electron microscope, and then quantitatively studied the distribution characteristics of the pore and throat sizes by combining with the capillary pressure curve, pore and throat distributions and structural parameters, and summarized the pore-throat assemblage patterns in the study area. The pore morphology in the study area is complicated, with an average face porosity of 2.18%, and the types mainly include original pores (residual intergranular pores), secondary pores (microfractures, feldspar dissolution pores, rock fragment dissolution pores, and intercrystalline micropores), and mixed-causal intergranular pores, among which dissolution pores and residual intergranular pores are the most developed; and the types of throats mainly include necked, lamellar, curved lamellar, and tubular. The pore-throat assemblage patterns are classified into: (I) residual intergranular pore/mixed causal intergranular pore—necked throat assemblage, (II) residual intergranular pore/feldspar dissolution pore—lamellar/curved lamellar throat assemblage, (III) feldspar dissolution pore/rock fragment dissolution pore—curved lamellar/tubular throat assemblage, and (IV) intercrystalline pore—tubular throat, with the reservoir space and pore-throat connectivity deteriorating in turn. Pore and throat characteristics and assemblage patterns play a decisive role in the reservoir's storage performance and seepage capacity. Fine characterization of the pore and throat of the target formation in the study area was achieved based on microscopic experimental data, which will provide a substantial basis for fine classification of the reservoir at a later stage.