Coal-to-methanol is one of the key industries of cleaner production audit. Using SimaPro software, the life cycle assessment of main units such as gasification, methanol, boiler and air separation in the coal-to-methanol project（coal-water slurry process） of an enterprise in Shaanxi was carried out. Eleven indicators were selected for environmental impact assessment, and the calculation of characterization, damage assessment, standardization, weighting and process contribution was carried out. The correlation between environmental impact and unit process was analyzed from the characteristics of resource and energy use and pollutant emission.The results show that in the whole life cycle of coal-to-methanol, the comprehensive impact of gasification unit on the environment accounts for 74.7%, methanol unit accounts for 24.7%, followed by air separation unit and boiler unit. For a single indicator, the gasification unit has the largest impact on carcinogens, respiratory organic matter, respiratory inorganic matter, radiation, ozone layer,ecotoxicity, acidification/eutrophication, land use, minerals and fossil fuels, and the methanol unit has the largest impact on climate change.