NOVELTY - The device comprises a penetrating fluid tank, a mechanical grizzly screen connected with the penetrating fluid tank through a first pipeline, a tank connected with the mechanical grizzly screen, a lime milk groove connected with the tank through a second pipeline, an ammonia nitrogen stripping tower connected with the tank through a third pipeline and provided with a fan, an acidification tank connected with the ammonia nitrogen stripping tower, and an ammonia gas recovery tower connected with ammonia nitrogen stripping tower through a fourth pipeline and provided with a vent-pipe.    USE - The device is useful for treating leachate during the biomass landfill process (claimed).    ADVANTAGE - The device allows effective, economical and simple treatment of leachate without causing pollution to water body.    DETAILED DESCRIPTION - The device comprises a penetrating fluid tank, a mechanical grizzly screen connected with a penetrating fluid tank through a first pipeline, a tank connected with the mechanical grizzly screen, a lime milk groove connected with the tank through a second pipeline, an ammonia nitrogen stripping tower connected with the tank through a third pipeline and provided with a fan, an acidification tank connected with the ammonia nitrogen stripping tower, an ammonia gas recovery tower connected with ammonia nitrogen stripping tower through a fourth pipeline and provided with a vent-pipe and an ammonium sulfate recycling pipe, a sulfuric acid groove connected with the ammonia gas recovery tower through a fifth pipeline and connected with the acidification tank through a sixth pipeline, an anaerobic reactor connected with the acidification tank through a seventh pipeline, a methane recovery tower connected with the anaerobic reactor through a eighth pipeline, a sedimentation tank connected with the anaerobic reactor through a ninth pipeline, a biological contact oxidation tower connected with the sedimentation tank through a tenth pipeline, a secondary sedimentation tank connected with the biological contact oxidation tower, a reverse osmosis membrane device connected with a secondary sedimentation tank through a eleventh pipeline, and a finished product water tank connected with the reverse osmosis membrane device. The methane recovery tower is provided with a methane outlet and a waste gas discharging opening. The anaerobic reaction tank, the sedimentation tank and the secondary sedimentation tank are connected with a through L-shaped pipeline. A sludge pump is connected with a thirteenth pipeline and a fourteenth pipeline. A sludge concentration tank is connected with the sludge pump. A dewatering device is connected with the sludge concentrating tank. The sludge concentration tank and the dewatering device are connected with the sludge pump through the second pipeline. A leachate pump connected with the sludge concentration tank and the dewatering device through O-shaped pipeline and P-shaped pipeline. The first, third, seventh, ninth, tenth, eleventh, O-shaped pipeline and P-shaped pipeline are provided with a control valve. The third, seventh and seventh pipelines are provided with a percolate pump. The L-shaped pipeline and thirteenth and fourteenth pipelines are provided with a sludge pipeline control valve. An ammonium sulfate recycling pipe is provided with an ammonium sulfate recycle valve and an ammonium sulfate recycle pump. The second pipeline is provided with a lime emulsion control valve. The fifth and sixth pipelines are provided with a sulfuric acid solution control valve. The fifth pipeline is provided with a sulfuric acid pump. The eleventh pipeline is provided with a high pressure pump. The eighth pipeline is provided with a gas control valve. The methane recovery tower is provided with a methane control valve, and a waste gas discharging valve. The finished product is provided with a drain valve. The sludge concentration tank has a diameter of 5-20 m, and is provided with a stirrer. An INDEPENDENT CLAIM is included for a method for treating leachate during the biomass landfill process.