The invention provides a high-pressure easy-flash-evaporation mixed liquid sampling device which comprises a liquid inlet device, a primary pressure relief valve, a primary gas-liquid separator, a gas-phase branch device, a liquid-phase branch device and a sampling bottle, wherein an outlet of the liquid inlet device is connected with an inlet of the primary pressure relief valve; an outlet of the primary pressure relief valve is connected with an inlet of the primary gas-liquid separator; a gas-phase outlet of the primary gas-liquid separator is connected with the gas-phase branch device; a liquid-phase outlet of the primary gas-liquid separator is connected with the liquid-phase branch device; the sampling bottle is connected with the liquid-phase branch device; the liquid-phase branch device comprises a gas-liquid mixture separator and a heavy component secondary pressure relief valve; and the gas-phase branch device comprises a gas-phase condenser, a light component gas-liquid separator, a light component secondary pressure relief valve and a secondary gas-phase gas-liquid separator. The high-pressure easy-flash-evaporation mixed liquid sampling device has the advantages of high separation efficiency, excellent performance, high safety, environment friendliness, high stability and long service life.