This paper introduces the salting-out technology of ethanol, acetone and n-butanol in the crude alcohol after the bio-butanol fermentation liquid is processed by the mash tower. Aiming at the problems of low total solvent concentration, difficult recovery and high energy consumption for the bio-butanol fermentation broth separation, this paper studied the effects of unsaturated composite salts, salting-out temperature, and the volume ratio of salting-out agent to crude alcohol on the water removal of bio-butanol system. According to the index of water content in the organic phase, the most beneficial salting-out agent for water removal was selected from various composite salts. A salting-out extractant composed of water and composite salts was developed. The results showed that the extraction effect of unsaturated salt was not good for n-butanol-acetone-ethanol-water system. The n-butanol-acetone-ethanol-water system is extracted with a composite salt and water extractant, which can increase the mass fraction of n-butanol, acetone and ethanol, and achieve the purpose of separating and concentrating n-butanol, acetone and ethanol. After the primary countercurrent extraction, the mass fraction of n-butanol in the organic phase increased from 26% to over 64%, the mass fraction of acetone increased from 10% to over 21%, and the mass fraction of ethanol increased from 4% to over 9%. The composite salting-out agent can achieve the purpose of efficient water removal.