The invention relates to lignin serial coal water slurry dispersing agent and a preparation method thereof, and belongs to the technical field of dispersing agent which is prepared by coal water slurry. The dispersing agent comprises the following raw material components in parts by weight: 1,000 parts of alkali lignin, 20 to 50 parts of polyethylene glycol, 2 to 10 parts of carboxylic acid, 1 to 5 parts of concentrated sulfuric acid, 0.1 to 1 part of hydroquinone, 20 to 60 parts of acrylic acid, 60 to 150 parts of vinyl monomer, 200 to 400 parts of sodium sulfite, 300 to 500 parts of acetaldehyde solution, 30 to 50 parts of oxidant and 10 to 20 parts of reducing agent. Compared with the prior art, the lignin serial coal water slurry dispersing agent adopts the alkali lignin as a raw material, so that the cost is reduced, the average molecular mass of the lignin is remarkably improved, the hydrophily is obviously enhanced, and the dispersing effect is prominently improved; and in addition, the dispersing agent has the advantages of low cost, simple preparation technique, more generality of raw materials, wide sources of the raw materials, cheaper price and good modifying effect; and the resource utilization is implemented for wastes, so that the environmental pollution from the wastes is reduced.