The invention provides a scale inhibition dispersant and a preparation method thereof. The scale inhibition dispersant is prepared by polymerization reaction of maleic anhydride, water, a sulfonic acid monomer, a carboxylic acid polymerization monomer, phosphate and an initiator. Different from other methods, the method provided in the application adopts copolymerization of the maleic anhydride, the sulfonic acid monomer, the carboxylic acid polymerization monomer and the phosphate, controls the addition modes and amounts of the monomers, The addition mode and amount of the initiator are regulated and controlled, the polymerization process is stabilized, and the quadripolymer scale inhibition dispersant is prepared; the molecular structure of the prepared scale inhibition dispersant contains carboxylic acid groups, sulfonic acid groups and phosphonic acid groups, the prepared scale inhibition dispersant has strong scale inhibition and dispersion performance and temperature resistance;and when the scale inhibition dispersant is applied to coal gasification black ash water treatment, scale formation and deposition of the system can be effectively slowed down, and operation time of equipment can be prolonged.