The invention belongs to the technical field of sludge reduction for cold rolling pickling wastewater in the steel industry, and discloses a method for sludge reduction for the cold rolling pickling wastewater in the steel industry. In the method disclosed by the invention, neutral salt wastewater and wastewater mixed with acid are completely and separately treated to obtain sludge containing hazardous wastes and general sludge respectively, and the sludge output of each unit is reduced by accurately adding chemical agents at each unit; in the technology for treating the neutral salt wastewater, caustic soda liquid is respectively added in a first stage neutralizing tank and a second stage neutralizing tank; in the technology for treating the wastewater mixed with acid, the treatment is performed by using a lime and austic soda liquid combination method; and in the treatment of a neutralizing tank, the pH value is controlled between 1.5 and 3.0, and the pH value during neutralizationreaction is controlled between 8.2 and 8.7; and a flocculation process is adopted after the neutralization reaction, polyaluminum chloride, polyacrylamide and other flocculants are added for reactingand are mixed so as to enlarge pollutant particles. By use of the method, the output water can stably reach the standard, and the water treatment cost per ton is reduced.