The invention discloses a process for producing liquefied natural gas by coal bed gas in mine coal, comprising the following steps: feeding the coal bed gas in the mine coal after oxygen removal, pressurization, desulphurization, decarburization and drying treatment in a low temperature device to serve as a feed gas for low temperature separation, respectively obtaining waster nitrogen and methane gas after separation, feeding the methane gas obtained by low temperature separation in a refrigerating liquefaction plant for refrigeration and liquefaction, and obtaining the liquefied natural gas. In the process of the invention, the coal bed gas in the mine coal with a low methane content is utilized as the feed gas to produce the liquefied natural gas (LNG) with high methane content up to above 99%. The invention has simple process flow, less equipment input and maintenance cost, and can reduce power consumption of circulation and compression.