Syngas enters the activated carbon adsorber and tube reactor where the crude methanol is produced. After being cooled in the heat exchanger and cooler, the crude methanol-containing gas quickly enters crude methanol separator where the crude methanol is condensated. The condensated crude methanol is sent to distillation unit. DME, methyl formate, and other low-boiling impurities are separated in the first fractionation column, and then the fine methanol is produced after water and miscellaneous alcohol are removed in the second fractionation column.