The invention discloses a macromolecule class dispersing agent, and a preparation method and an application thereof. The novel dispersing agent is prepared by employing acrylic acid as a main reaction monomer, adding one or more monomers such as methacrylic acid, maleic anhydride, fumaric acid, itaconic acid and sodium methyl allyl sulfonate as comonomers; allowing lignosulfonate recycled from papermaking wastewater to participate in polymerization; taking a redox system as an initiation system; performing water solution polymerization; and neutralizing with alkaline substance. The novel dispersing agent allows the grinding of calcium carbonate to have the characteristics of low pulp viscosity, small grain size, good dispersibility and high stability.