The tight sandstone reservoirs of the Shanxi Formation in the Daning–Jixian block of the Ordos Basin are characterized by strong microscopic heterogeneity and complex gas–water relationships, which limit detailed reservoir characterization. The multi-scale pore–throat structures of reservoirs are difficult to characterize effectively using conventional methods. thin-section analysis, scanning electron microscopy, high-pressure mercury injection, and nuclear magnetic resonance experiments were conducted. Based on T2 spectral characteristics, a three-segment fractal model for micropores, mesopores, and macropores was constructed. Quantitative relationships between fractal dimensions and petrophysical and mercury injection parameters were established, A comprehensive reservoir quality index coupling microscopic pore–throat structures with macroscopic seepage characteristics was developed to support fine reservoir classification and quantitative evaluation. The results show that the reservoirs are mainly composed of lithic quartz sandstone. The pore structure is strongly modified by clay mineral filling and illite bridging. Primary pores are largely destroyed. Secondary dissolution pores become the dominant storage space. Reservoir properties are significantly constrained by complex pore–throat structures. A comprehensive reservoir classification and evaluation criterion is established based on multi-scale pore–throat structure characterization results and the comprehensive reservoir quality index. The reservoirs are classified into three categories. Class II reservoirs are further subdivided into two types. The reservoir quality is ranked in descending order as Class I, Class IIa, Class IIb, and Class III.These results provide important geological evidence for tight sandstone reservoir classification and sweet spot prediction in the study area.