The invention relates to a method and system for producing liquefied natural gas through coke oven gas cryogenic separation. According to the different boiling points of all the components in a coke oven gas, the coke oven gas is cooled level by level, all the component gases in the coke oven gas are sequentially extracted according to the different boiling points, the extracted liquid methane, ethylene and ethane are mixed, and the liquefied natural gas is produced. By the adoption of the method and system, the procedure is simple, operation is convenient, investment is small, energy consumption is low, and economic benefits are high.