NOVELTY - Methane (CH4) is extracted from coke oven gas by conducting crude desulfurization and pretreatment to coke oven gas; hydrolyzing and removing hydrogen sulfide (H2S); removing carbon dioxide (CO2) by N-methyldiethanolamine wet method; removing sulfide, mercury, water and high carbon compounds by absorption method; entering coke oven gas into film separation device to separate hydrogen, CH4, nitrogen (N2), and carbon monoxide (CO); and entering coke oven gas into low temperature rectification tower, and extracting liquid methane from bottom of tower.    USE - Method of extracting methane from coke oven gas (claimed).    ADVANTAGE - The method has simple technique and high purity of product.    DETAILED DESCRIPTION - Extraction of methane from coke oven gas comprises:    (A) compressing and cooling coke oven gas collected from production of coke at 0.12-0.15 MPa and 20-40 degrees C; removing components of sulfur, benzene, naphthalene and tar impurity by crude desulfurization and pretreatment;    (B) compressing the coke oven gas after crude desulfurization and pretreatment at 2.2-4 MPa, hydrolyzing and removing hydrogen sulfide (H2S);    (C) removing CO2 from coke oven gas after hydrolyzing by using N-methyldiethanolamine wet method and reducing content of CO2 in the coke oven gas to trace amount;    (D) removing sulfide, mercury, water and high carbon compounds (more than 5C) from the CO2-removed coke oven gas by using absorption method;    (E) entering the coke oven gas with pressure of 1.5-4 MPa and temperature of 20-60 degrees C into a film separation device; separating hydrogen, CH4, N2, and CO in the gas after passing the film separation device such that substances of hydrocarbon components in the coke oven gas after removing hydrogen are 40-80%;    (F) entering the hydrogen-removed coke oven gas with temperature of 20-60 degrees C and pressure of 1.5-4 MPa into a plate type heat exchanger; reducing temperature and removing substances with boiling points more than - 50 degrees C and residual in the coke oven gas; and    (G) entering the coke oven gas into a low temperature rectification tower; carrying out heat exchange and mass exchange in the low temperature rectification tower; moving gas substance to top of tower and running liquid substance to bottom of tower; and extracting liquid substance from bottom of tower, where the gas substance extracted from the top of tower is mixture of nitrogen, hydrogen and carbon monoxide gas containing little methane; the liquid substance extracted from the bottom of the tower is liquid methane from mixture of methane (C1), ethane (C2) and propane (C3) and with purity of 98%; content of carbon monoxide is less than 0.5%; and where the liquid methane is warmed to gas phase to obtain methane gas.