The invention provides a technical method for preparing low-carbon mixed alcohol by a synthetic gas one-step method from coal, which comprises the following specific steps that coal is gasified, the gas is purified, and desulfurizing is conducted by a chemical adsorption method to obtain synthetic gas consisting of hydrogen and carbon; then the synthetic gas is in contact with a Cu-based sulfide catalyst under the condition of high pressure for a catalytic reaction, the reacted gas is subjected to heat exchange, condensation and liquid separation, a liquid-phase component and tail gas are obtained, the liquid-phase component is low-carbon mixed alcohol, and the low-carbon mixed alcohol mainly containing alcohols and a small amount of C1-C4 gaseous hydrocarbon are generated through catalytic synthesis. According to the method, the coal is used as the raw material to synthesize the low-carbon mixed alcohol, the final products are the low-carbon mixed alcohol and the C1-C4 gaseous hydrocarbon, the low-carbon mixed alcohol is used as the chemical raw material, the C1-C4 gaseous hydrocarbon is used as the fuel, the final products are not wasted, and pollution is avoided. The Cu-based sulfide catalyst is used as the catalyst, such that the disadvantage of low activity of the existing catalyst is changed, and the production speed of the low-carbon mixed alcohol is improved.