The extraction of shale oil and gas has gradually become the focus of attention in the world energy industry. Currently, the understanding of the fluid flow mechanism of multi-scale pore fracture systems in shale reservoirs with natural fractures is still unclear. Therefore, this article processed simulated natural fractured rock cores with different fracture openings and fracture densities through wire cutting and placement of metal gaskets. Fluid flow experiments were conducted under different displacement pressure differentials, and fluid flow patterns within natural fractures in shale oil reservoirs were summarized and analyzed. The results show that: For gas flow within natural fractures, the gas permeability of the core is significantly higher in the low-pressure range than in the high-pressure condition due to the gas-slip effect. The low-velocity flow of fluid within a natural fracture has a nonlinear segment and a linear segment. The nonlinear characteristics decrease with the increase of fracture opening and fracture density, and increases with increasing fluid viscosity. With the increase of the displacement pressure, the influence of inertia force on the fluid flow gradually plays a dominant role. The resistance coefficient decreases with the increase of reynolds number, and the two maintain a linear relationship in the double logarith-mic coordinate axis.