The invention provides a process for producing liquefied natural gas, which comprises the following steps of: introducing purified feed gas into a first heat exchanger for precooling; introducing the precooled feed gas into a heavy hydrocarbon separator for gas-liquid separation; introducing the separated gaseous fluid into a second heat exchanger, and liquefying to obtain liquid-state fluid; and depressurizing and throttling to obtain the liquefied natural gas, wherein a refrigeration cycle consists of two independent mixed working medium refrigeration cycles in a high temperature area and a low temperature area; the feed gas can pass through a reversing heat exchanger to enter the first heat exchanger; and the separated heavy hydrocarbons and BOG return to the heat exchanger for reheating. In the process, the energy consumption is low; each mixed working medium refrigeration cycle is controlled by only one throttle valve in a cold box, and the operation is simpler; due to the reversing heat exchanger, the production process is more stable and safe; and the cold quantity of the separated heavy hydrocarbons and BOG is fully recycled and discharged out of the cold box, and the energy consumption is reduced.