NOVELTY - Purifying landfill leachate anaerobic marsh gas, comprises (i) performing anaerobic fermentation of landfill leachate; (ii) removing moisture-particulate methane in centrifugal dehydrator I; (iii) pressurizing landfill leachate anaerobic marsh gas; (iv) separating liquid hydrogen sulfide gas, and removing refined hydrogen sulfide; (v) removing organic sulfur gas; (vi) removing methane in volatile organic compounds (VOCs); (vii) removing particulate methane and liquid particles; (viii) performing freeze-drying; (ix) heating; and (x) heating gas, and transferring to membrane separation system.    USE - The method is useful for purifying landfill leachate anaerobic marsh gas (claimed).    ADVANTAGE - The method effectively reduces water vapor content of biogas; and has high purification efficiency reaching up to 99.9% and recovery rate reaching upto 99%.    DETAILED DESCRIPTION - Purifying landfill leachate anaerobic marsh gas, comprises (i) carrying out anaerobic fermaentation of the landfill leachate in a anaerobic tank, producing biogas, closing the anaerobic tank with a lid, adding water through the pipeline to the anaerobic tank, washing, removing gas and dust in water, and then transferring to a centrifugal dehydrator I; (ii) removing moisture and particulate methane in centrifugal dehydrator I, and transferring to a roots blower; (iii) pressurizing the landfill leachate anaerobic marsh gas in roots blower, and transferring to a wet desulfurizing tower for crude hydrogen sulfide removal; (iv) transferring the landfill leachate anaerobic marsh gas into a centrifugal dehydrator II, after crude hydrogen sulfide removal, separating liquid hydrogen sulfide gas and transferring to a dry desulfurization tower for the refined hydrogen sulfide removal; (v) transferring the marsh gas into a dry organic sulfur tower for removing organic sulfur gas; (vi) transferring the marsh gas to a volatile organic compounds(VOCs) removal device for removing methane in VOCs; (vii) transferring the marsh gas into an air inlet buffer tank having stable pressure and flow rate for removing particulate methane and liquid particles; (viii) carrying out freeze drying in a freeze drier having dew point of gas reducing to 2-8 degrees C; (ix) transferring the marsh gas into a dry screw compressor, under pressurized condition, and transferring the pressurized gas into the gas purification system, and sequentially passing the biogas through oil separator, cooler, refined filter, and heating the device using a heater; and (x) heating the gas at 20-35 degrees C, and transferring to membrane separation system, where the system comprises three separate settings. The main process steps of the separation includes (a) passing the gas to be separated to the first-stage membrane group, and the trapped gas (product gas) is then passed into the second-stage membrane group for the continuous separation, (b) passing the trapped gas into the second-stage membrane group, separating, to obtain a highly concentrated methane gas product, (c) passing the discharge gas (exhaust gas) of the first-stage membrane group to the third-stage membrane group, separating and recycling methane, and refluxing the trapped gas, (d) mixing the discharge gas from the third-stage membrane group and the second-stage membrane group, refluxing back the gas to the pre-pressurized inlet, recycling methane residue, which also plays a role in regulating intake air flow rate, and (e) directly discharging the discharge gas emissions to third-stage membrane group, separating the biogas from the third-stage membrane group under reduced pressure, and carrying on to the natural gas pipeline network or pressurized compressed natural gas (CNG) carrier.