The invention belongs to a device for producing methanol by medium and low pressure combined alcohol and single alcohol. The device comprises a gasification system and a steam system, wherein the gasification system is connected with a raw gas inlet of a shift converter; the steam system is connected with a steam inlet of the shift converter; a gas outlet of the shift converter is connected with a shell pass inlet of a heat exchanger through a gas supplementing oil-water separating device; a shell pass outlet of the heat exchanger is connected with a tube pass inlet of a medium-pressure-method methanol synthesis tower; a tube pass outlet of the upper part of the medium-pressure-method methanol synthesis tower is connected with a raw material gas inlet of a low-pressure synthesis tower; a reaction gas outlet of the bottom of the low-pressure synthesis tower is connected with a shell pass inlet of the bottom of the medium-pressure-method methanol synthesis tower; a shell pass outlet of the top of the medium-pressure-method methanol synthesis tower is connected with a tube pass inlet of the heat exchanger; a tube pass outlet of the heat exchanger is connected with an alcohol-separation and alcohol-washing two-in-one tower; and the bottom of the alcohol-separation and alcohol-washing two-in-one tower is connected with a methanol storage tank. The device has the advantages that the synthesis ammonia product is greatly transformed into methanol products, the production capacity of the methanol is improved, and the integral production structure of enterprises is optimized.