The invention relates to a method and a device for efficiently liquefying and recovering natural gas. The method is characterized in that liquid nitrogen and natural gas are different in boiling point, freezing point, saturation temperature and pressure, and on that basis, natural gas can be directly charged into a cryogenic vessel which is filled with liquid nitrogen; the natural gas and the liquid nitrogen in the same cryogenic vessel are directly mixed, exchange heat and then are liquefied to obtain LNG (Liquefied Natural Gas); the saturation pressure of liquid in the cryogenic vessel is controlled to prevent the natural gas from solidifying and icing as well as effectively separating the LNG and the liquid nitrogen. The method and the device have the main advantages that equipment investment cost is low, and the LNG can be normally used; the method and the device can be widely applied to the liquefaction of a micro gas source, and particularly suitable for BOG recovering during LNG refilling.