The pore structure not only determines the microscopic characteristics of tight oil reservoirs, but also controls the macroscopic physical properties of the reservoir, which is the key to restricting the storage and permeability of oil and gas in the reservoir. This investigation focuses on core samples from twelve tight oil reservoirs located in the Yanchang Formation within the Wuqi region of the Ordos Basin. The experiments include core thin section analysis, scanning electron microscopy, and high-pressure mercury injection, the study qualitatively and quantitatively elucidates the pore structure characteristics. Furthermore, mathematical fractal theory is utilized to meticulously assess the fractal nature of the reservoir pore throat. The findings indicate that: (1) Reservoirs can be categorized into three distinct types based on the morphology of the mercury intrusion curves and pore structural parameters, with Type I exhibiting micro-scale fractures and residual intergranular pores, while Type III is distinguished by nano-scale dissolution pores. (2) The pore size distribution among the core samples varies from 0.002 to 6.12 μm, demonstrating both unimodal and bimodal morphologies, a diversity of pore types, a broad size distribution, and significant heterogeneity. (3) The fractal curve for pore throats displays a distinctive multi-segment pattern, classifying the pore throat system into three categories: large, medium, and small, with demarcation points at 0.1 μm and 1.0 μm. (4) The fractal dimensions of pores within different pore throat ranges follow the sequence D1(4.56) > D2(2.99) > D3(2.24), where larger fractal dimensions correlate with more prominent pore throat radius, often encompassing residual intergranular pores and micro-fractures lacking fractal traits. The varied development of pore types and sizes results in substantial heterogeneity in the pore structure, which correlates with physical properties and pore structural parameters. Additionally, variations in mineral composition and content add to the inherent complexity of the pore structure, directly affecting reservoir quality and efficient exploitation during subsequent phases.