TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Processes: The method further comprises introducing one part of treated coal to gasification furnace from synthesis gas methanation section of gasification furnace. The pre-oxidization is performed at 100-300 degrees C under 0-6 MPa for 1-8 hours. The ion exchange is performed at 100-300 degrees C under 0-6 MPa, pH 7-14 for 1-8 hours. The temperature of coal methanation section is 500-700 degrees C; and the temperature of the synthesis gas methanation section is 400-800 degrees C. The temperature of coal pyrolysis section is 500-600 degrees C. The pressure in gasification furnace is 3-4 MPa. The coal is replaced by petroleum coke or biomass. Preferred Components: The at least one part of coal methanation catalyst is alkali metal cation or alkaline earth cation exchanged to coal surface; the other parts comprising substances introduced from coal methanation section of gasification furnace and/or synthesis gas methanation section and/or synthesis gas generating section to gasification furnace comprising alkali carbonate, alkali hydroxide, alkali oxide, alkaline earth carbonate, alkaline earth hydroxide or alkaline earth oxide. The first oxidant is oxygen, air, peroxide, permanganate or hypochloride. The synthesis gas methanation catalyst is sulfur tolerance methanation catalyst comprising molybdenum sulfide, molybdenum oxide, cobalt oxide, loaded on aluminum oxide or zirconium oxide carrier, or eutectic mixture of molybdenum-containing compound, cobalt-containing compound and nickel-containing compound. The gas oxidant is steam and oxygen, or steam and air. The temperature of generating synthesis gas is 800-1200 degrees C. The mass ratio of steam in gas oxidant to coal is 0.5-5; and mass ratio of the oxygen in gas oxidant to coal is 0.1-1. The coal is bitumite, anthracite or lignite. The coal is coal powder with particle size of 0.01-10 mm.    TECHNOLOGY FOCUS - METALLURGY - Preferred Components: The alkali metal cation is potassium ion and/or a sodium ion; and alkaline earth cation is calcium ion and/or magnesium ion.