The invention discloses a method for preparing a powdery polycarboxylic acid hyperdispersant. The method comprises the following steps of: a) adding superfine inorganic powder or sol into solution of polycarboxylic acid polymer and uniformly mixing to obtain polycarboxylic acid slurry, wherein the solid content of the solution of polycarboxylic acid polymer is 10 to 60 percent, and the weight ratio of the superfine inorganic powder or sol to the solution of polycarboxylic acid polymer is 0.001 to 20; and b) forming atomized droplets from the polycarboxylic acid slurry which is obtained in the step a by using an atomizer, and introducing the atomized droplets into a dying chamber to dry and dewater; and when the polycarboxylic acid slurry is atomized and dried, simultaneously adding an inorganic separant into the dying chamber to prevent the formed powder from sticking to walls and caking so as to obtain the powdery polycarboxylic acid hyperdispersant. The product obtained by the invention has the advantages of high neat cement paste dispersibility, high dispersion stability and high anti-caking performance.