The invention discloses a method for preparing a sulfonation condensation polymerization modified humic acid water-coal-slurry dispersing agent. The method comprises the following steps: stirring to dissolve humic acid and urea in water, adding an alkali adjusting agent, further adding a sulfonating agent, heating to 50-55 DEG C, starting dropping a mixture solution of acetone and formaldehyde, controlling the temperature at 55-60 DEG C, stopping adding within about 1-1.5 hours, further heating to 70-80 DEG C, reacting for 1-2 hours at constant temperature, continuously heating to 95-110 DEG C, performing polymerization reaction for 2-3 hours, subsequently cooling and discharging a material, drying and crushing the material so as to obtain a sepia solid powder product. The dispersing agent is a humic acid series water-coal-slurry dispersing agent which contains groups of sulfonyl, carboxyl, hydroxyl, methyl and the like, on the basis that the good dispersity of the humic acid dispersing agent is maintained, the stability is improved, the method disclosed by the invention is simple, the raw materials are easily available, the reaction condition is gentle, and a product can be used for well solving the problem that the stability is poor when the humic acid is used as the water-coal-slurry dispersing agent.