NOVELTY - Pyrolysis gas product, semi-coke gasified synthesis gas and biomass-gasified synthesis gas are mixed, Fischer-Tropsch synthesis reaction is carried out, and separated to obtain synthetic oil and unconverted gas. The synthetic oil and tar are mixed, and introduced into hydrocarbon recovery distillation tower. The light hydrocarbon and unconverted gas are pressurized, and gas mixture containing carbon monoxide, hydrogen, carbon monoxide, methane, ethane, ethylene, propane, isobutane, butane and butene is obtained.    USE - Synthesis of methane, gasoline and diesel (claimed).    ADVANTAGE - The method enables economical synthesis of methane, gasoline and diesel.    DETAILED DESCRIPTION - A low-grade coal is processed, solid product char and gas product are obtained, and pyrolysis gas product and tar is separated from gas product. Semi-coke gasification of solid product is carried out, to obtain semi-coke gasified synthesis gas. Biomass gasification of solid product is carried out, to obtain biomass-gasified synthesis gas. The pyrolysis gas product, semi-coke gasified synthesis gas and biomass-gasified synthesis gas are mixed, Fischer-Tropsch synthesis reaction is carried out at 310-370 degrees C in presence of catalyst, and oil and gas separation is carried out to separate synthetic oil and unconverted gas. The synthetic oil and tar are mixed, introduced into hydrocarbon recovery distillation tower at less than 180 degrees C fraction, 180-320 degrees C fraction and more than 320 degrees C, respectively, hydrotreatment process is performed at 350-500 degrees C under pressure of 35-65 atmosphere using silicon dioxide-aluminum oxide catalyst, and 4C light hydrocarbon, 5-6C component, 7-12C component and/or 13-20C component as diesel preliminary product are collected. An isomerization component as additive is added to 5-6C component to improve gasoline octane number, and isomerized at 320-450 degrees C under pressure 30-40 atmosphere of using isomerization catalyst. A hydrogenation component as an additive is added to 7-12C component to improve gasoline octane number, and catalytic reforming reaction is carried out at 350-500 degrees C under pressure of 30-40 atmosphere using platinum/L-type zeolite catalyst. Hydrocracking more than 320 degrees C fraction using magnesium silicate zeolite as catalyst at 400-600 degrees C under pressure of 35-65 atmosphere. The obtained product is divided into less than 4C light hydrocarbon gas, 5-6C components and hydrotreated less than 180 degrees C fraction, 13-20C component as diesel preliminary product, and remaining components are subjected to non-catalytic hydrogenation reforming at 300-500 degrees C under pressure of 25-45 atmosphere. The light hydrocarbon and unconverted gas are pressurized under pressure of 25 atmosphere after gas methanation, and gas mixture containing 15-25 vol.% carbon monoxide, 20-30 vol.% hydrogen, 30-40 vol.% carbon monoxide, 7-15 vol.% methane, 5-10 vol.% ethane, 3-5 vol.% ethylene, 2-4 vol.% propane, 1-3 vol.% isobutane, 0.5-2 vol.% butane and 0.5-2 vol.% butene is obtained. The mass ratio of biomass and low-grade coal in the solid product is 0.5-1.5. The catalyst is cobalt and/or ruthenium-based catalyst, preferably ruthenium, titanium dioxide, cobalt, zirconium, silicon dioxide and/or magnesium oxide, more preferably ruthenium/titanium dioxide, cobalt/zirconium/silicon dioxide or cobalt/magnesium oxide/silicon dioxide. The isomerization catalyst is boron oxide-aluminum oxide catalyst. An INDEPENDENT CLAIM is included for system for synthesizing methane, gasoline and diesel, which consists of a low-grade coking unit, coal tar recovery equipment, a semi-coke gasification unit, a biomass gasification unit, a synthesis gas mixer, a Fischer-Tropsch synthesis reactor, an oil splitter, an oil refining unit, a feed gas mixer and a methanation reactor.