The invention discloses a two-stage medium-pressure screw-type air compressor set, comprising a first-stage screw compressor and a second-stage screw compressor, wherein the upper part of the first-stage screw compressor is provided with an air inlet; the lower part of the second-stage screw compressor is provided with an exhaust chamber which is communicated with a gas-liquid separator via a tangential gas-liquid inlet tube; the middle part of the gas-liquid separator is provided with a separated oil outlet tube; lubricating oil is injected to the lubricating part of the compressor via an oil-liquid filter; the rear part of the gas-liquid separator is provided with a secondary separator for secondarily separating moisture in the oil liquid; the secondary separator comprises an upper separating barrel and a lower separating barrel, wherein the upper part of the upper separating barrel is provided with a secondary oil inlet connected with an oil outlet tube, the lower part thereof is provided with a secondary oil outlet which is connected with the lubricating part of the compressor, an electric ball valve is arranged between the upper separating barrel and the lower separating barrel, the lower part of the lower separating barrel is provided with a secondary drain valve, and all components are controlled by PLC. The invention has the advantages of being capable of furthest lowering moisture and impurities in the lubricating oil, thereby having stable pressure elimination, high operation efficiency, good using reliability and safety, low noise and long service life.