Abstract: The blended-wing-body configuration refers to the full lift surface aircraft shape that greatly integrates the wing and fuselage, demonstrating significant performance advantages and development potential in improving cruise efficiency, reducing emissions, and reducing noise. Using Reynolds averaged Navier-Stokes method and body force model based on blade element momentum theory, the separation flow field under the effect of boundary layer ingestion caused by the distributed propulsion installed on the civil blended-wing-body aircraft was preliminarily investigated. Firstly, the distributed BLI propulsion configuration of the civil aircraft with a blended-wing-body layout was simplified to the duct fan-wing segment coupling configuration, and three working conditions of duct fan, indicating that the mass flow rate is less than 1, equal to 1, or greater than 1, were calculated respectively. The details of the flow field and calculation accuracy and efficiency of sliding mesh method, frozen rotor method, and body force model method based on blade element momentum theory were compared and analyzed. Secondly, the distributed BLI propulsion -wing coupling configuration was established. Comparative analysis of the flow field around the distributed BLI propulsion -wing coupling configuration at different rotational speeds is conducted to explore and verify the ability of the distributed BLI propulsion system established in this paper to suppress separation. Finally, the distributed BLI propulsion was installed on the wing-body fusion section of NPU-BWB-300, a conceptual civil BWB aircraft, to explore its influence on the aerodynamic characteristics and separation flow field of NPU-BWB-300. The results show that the sliding mesh method, the frozen rotor method and the body force model method based on the blade element theory can all describe the flow field details of the boundary layer ingestion of the duct fan. The distributed BLI propulsion established in this paper has the ability of restraining separation, and its application to NPU-BWB-300 can also achieve a relatively obvious effect of improving the separation flow field.