Method and device for liquefying natural gas by using propylene precooling mixed cryogen

The invention provides a method and a device for liquefying natural gas by using a propylene precooling mixed cryogen, aiming at solving the problems that a heavy hydrocarbon component needs to be added in a natural gas precooling cryogen for ensuring cooling effect when propane is used as the natural gas precooling cryogen so as to result in that pipelines and equipment are blocked and normal circulation operation is influenced. According to the invention, propylene is adopted to replace propane to be used as the precooling cryogen in a natural gas liquefying process with a mixed cryogen, and the precooling effects of the natural gas and mixed cryogen are improved through changing process flow, thereby obviously reducing energy consumption and simplifying liquefication flow equipment andoperation.