NOVELTY - Garbage is sorted into organic garbage and inorganic garbage. The organic garbage is supplied to a reaction kettle, catalyst (I) is added, and the mixture is thermally decomposed. The produced cinder is discharged into a gasifier, and oil-gas mixture is supplied to a purification tower. Catalyst (II) is added to the gasifier and catalytic decomposition is carried out to produce fuel oil, sewage, and combustible gas. The fuel oil is collected, sewage is sent for treatment, and combustible gas is used for heating the reaction kettle.    USE - Extraction of fuel oil from building garbage.    ADVANTAGE - The method reduces burden of urban garbage, efficiently processes garbage solid waste without secondary pollution, and solves energy crisis by efficiently providing fuel oil.    DETAILED DESCRIPTION - Garbage is sorted into organic garbage and inorganic garbage. The organic garbage is supplied to a reaction kettle, catalyst (I) is added, and the mixture is heated at 200-295 degrees C and normal pressure for thermal decomposition. The produced cinder is discharged into a gasifier, and oil-gas mixture is supplied to a purification tower. Catalyst (II) is added to the gasifier and catalytic decomposition is carried out to produce fuel oil, sewage, and combustible gas. The fuel oil is collected, sewage is sent for treatment, and combustible gas is used for heating the reaction kettle. The oil-gas mixture is purified and supplied to a catalytic tower in which catalyst (III) is added for oil-gas mixture decomposition to convert a portion of oil-gas mixture into oil-water mixed liquid. The oil-water mixed liquid is separated into fuel oil and sewage. The fuel oil is collected and sewage is sent for treatment. Another portion of oil-gas mixture is supplied to condensing tower (I). The mixture in condensing tower (I) is condensed into oil-water mixed liquid, which is separated into fuel oil and sewage. The fuel oil is collected and sewage is sent for treatment. The remaining mixture in condensing tower (I) is returned to the reaction kettle to provide heat energy. The collected fuel oil is supplied to a catalytic reforming tower in which catalyst (IV) is added and heated at 100-195 degrees C and normal pressure, to obtain a mixed oil. The oil-gas mixture is sent to condensing tower (II), one portion is condensed into mixed oil and water-mixed oil, and water, fuel oil, and sewage are separated. The fuel oil passing through catalytic reforming tower is purified by passing through filters (I,II) and stored. The non-condensed mixed gas is combusted. The purification tower is provided with a top cover, a water canal, and an intake port on the top, and with a purification plate inside. The purification tower is provided with a dust inlet and outlet at the bottom. The upper portion of filter (I) is provided with an oil inlet, the lower portion is provided with an oil outlet opening, and the middle portion is a filtering layer from top to bottom in turns as sponge layer, steel wire mesh, steel plate screen, filtering material, sponge layer, and steel plate screen. The filters are provided with purifying materials, and have the same structure. Catalyst (I) comprises (in wt.%) calcium oxide (20-35), alumina (15-30), and water (15-20). catalyst (II) comprises calcium oxide (35-45), alumina (10-20), copper powder (20-30), and water (5-15). Catalyst (III) comprises calcium oxide (50-65), silica (15-20), low-temperature coke (5-10), and water (15-20). Catalyst (IV) comprises trisodium phosphate (20-35), magnesium trisilicate (45-55), and artificial zeolite (20-25).