This study investigates the pore structure of shale oil reservoirs in the Jimusaer sag of the Xinjiang Oilfield using high-pressure mercury intrusion experiments. Based on the experimental data, K-means clustering analysis is applied to categorize the pore structures. A single-phase permeability test method for shale oil core samples with varying pore systems is established. Additionally, a nonlinear mathematical model for single-phase flow based on the threshold pressure gradient is developed, along with an empirical formula for permeability related to pore structure characteristics, enhancing the understanding of single-phase flow mechanisms in shale oil reservoirs. The results indicate that the high-pressure mercury intrusion capillary pressure curve of the reservoir exhibits a plateau shape, suggesting a pore structure characterized by high drainage pressure and micro-nano pore throats, with good storage capacity but poor flow capability. The pore throat distribution is complex, often showing unimodal or bimodal characteristics; pore throat radii range from 0.005 μm to 9.19 μm. Class I pore throats are concentrated in the range of 0.02 μm to 0.57 μm, Class II in 0.01 μm to 0.04 μm, and Class III in 0.005 μm to 0.02 μm. The single-phase flow curves of shale oil cores exhibit typical non-Darcy flow characteristics, with a pronounced nonlinear relationship at low flow rates. The established cubic nonlinear mathematical model relating flow rate to pressure gradient effectively describes the nonlinear flow characteristics of shale oil cores. Moreover, the threshold pressure gradient increases as permeability decreases, exhibiting two stages of gradual and then rapid increase, with a variation range spanning three orders of magnitude.