TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The nickel-based catalyst comprises gamma -aluminum oxide and titanium dioxide as carriers and nickel oxide and lanthanum oxide as co-catalysts. The catalyst comprises (in wt.%) aluminum oxide (65-75), titanium dioxide (4-8), nickel oxide (15-25), lanthanum oxide (1.0-5) and chromium oxide (1-5). Preferred Method: The straw gas pressurized by the step (i) is directly filled in the converter of step (iii) by a straw gas path pipeline which is arranged in the pre-heater of the step (ii). The converted mixture gas output by the converter of the step (iii) enters the gas-liquid separator of the step (v) by the first section of the converted gas path pipeline, and the first section of the converted gas path pipeline is arranged in the condenser of the step (iv). The mixture gas processed by the gas-liquid separator of step (v) enters the adsorbing purifier of the step (vi) by the second section of the converted gas path pipeline to obtain the synthetic natural gas with methane content greater than 95% after processing of the adsorbing purifier. The converter is connected with the pre-heater after the first section of converted gas path pipeline is separated out from the converter, and then connected with inlet of the gas-liquid separator by passing through the condenser. The method further comprises purifying the pressurized straw gas by an adsorbing purifier after step (i) as mentioned above. The straw gas pressurized by the step (i) enters the adsorbing purifier by the straw gas path pipeline, and then enters the converter by the purified gas path pipeline. The purified gas path pipeline is arranged in the pre-heater. The converted mixture gas output by the converter enters the gas-liquid separator by the converted gas path pipeline, and the converted gas path pipeline is arranged in the condenser to obtain the synthetic natural gas with methane content greater than 95% after processing of the gas-liquid separator.