Abstract: Dynamic pressure oil-gas separators are widely used in new-type aero-engines due to their high separation efficiency and compact structure. A CFD numerical calculation model capable of describing the transition process from oil-gas bubbly flow to stratified flow was constructed to study the oil-gas separation law inside the oil tank. By analyzing the pressure field, velocity field of the oil tank and the velocity distribution law of the oil-gas separator, the coupled flow field characteristics of the oil tank and the oil-gas separator and the oil-gas separation mechanism were clarified. The research results show that a Rankine vortex structure with a forced vortex as the main body is formed inside the oil-gas separator, and the separation efficiency can exceed 90% by opening holes in the conical section. In addition, moving the ventilation hole of the oil tank to the far end of the oil-gas separator can effectively improve the ventilation efficiency.