The invention relates to techniques of recovery of light hydrocarbon through separation of natural gas, and discloses a natural gas liquefying method and device with a light hydrocarbon recovery function. The natural gas liquefying method comprises the steps of pre-cooling, separating light hydrocarbon, liquefying natural gas, recovering the light hydrocarbon and the like, wherein C2<+> in feed gas is respectively extracted and separated into qualified products by a rectification and separation method, and a refrigeration technical process is circulated by utilizing a mixed refrigerant, so that the liquefication of the natural gas and the recovery of the light hydrocarbon can be realized in the same device. According to the natural gas liquefying method and device with the light hydrocarbon recovery function, which are disclosed by the invention, by aiming at an air source with larger moisture proportion in a natural gas liquefying device, the C2<+> light hydrocarbon is recovered while LNG (liquefied natural gas) is obtained through the liquefication, so that the quality of the LNG can regulated, the influence of C3<+> component left in the LNG on the safety operation of a device in a deep cooling section is reduced, and cheap and high-purity chemical materials can be obtained.