The oil gas separation of the oil gas separator of a screw air compressor generally consists of a primary separation of the oil gas barrel and a secondary separation of the oil gas separator. The oil gas mixture coming out of the exhaust port of the air compressor host is mixed with large and small oil droplets and enters the oil gas barrel. Most of the oil in the oil gas mixture falls to the bottom of the tank under the action of centrifugal force and gravity, and compressed air containing oil mist (suspended oil particles with a diameter of less than 1um) is further subdivided through the micron and fiberglass filter layer of the oil gas separation filter. The diffusion effect of oil particles through the filter material, which is directly blocked by the filter material, and the mechanism of inertial collision and condensation, causes the suspended oil particles in the oil gas mixture to quickly condense into large oil droplets. Under the action of gravity, the oil accumulates at the bottom of the oil separation core, and returns to the lubricating oil system of the main engine through the inlet of the secondary oil return pipe at the bottom recess.