The invention relates to a coal water slurry additive technology, and is aimed at providing a coal water slurry additive for wastewater slurrying in the coal chemical industry and application of the coal water slurry additive in slurrying. The additive is prepared from, by weight, 10-20% of cetyl trimethyl ammonium bromide, 70-80% of formaldehyde condensate of sodium methyl naphthalene sulfonate and 10% of electrolyte. In use, positive ion and negative ion components, electrolyte, wastewater and the like in the additive are added in the slurrying process in two steps, and the prepared coal water slurry has the advantages of being high in concentration, low in viscosity and good in stability and rheological behavior; the preparation and application cost of the coal water slurry is reduced,the wastewater of the coal chemical industry is comprehensively used, the wastewater is turned into wealth, zero emission is realized, and remarkable economic benefits and environment protection significance are achieved. The prepared wastewater coal water slurry of the coal chemical industry can serve as gasification raw materials and combustion fuel, a large amount of organic matter in wastewater can be converted into effective components in synthesized gas during gasification reaction, and heat value and gasification efficiency are improved.