This invention reports a drug for hyperphospheremia and its preparative method. The preparation includes active constituents, lanthanum polystyrene sulfonate, and excipients. The preparative method in the invention can be summarized as follows: Polystyrene sulfonic acid is obtained by treating polystyrene sulfosalt with hydrochloric acid, soaked or eluted with water soluble lanthanum-contained solution, and washed with water till its PH is neutral. Then, the lanthanum polystyrene sulfonate solution is washed till the superfluous La− unexchanged is washed out. Lanthanum polystyrene sulfonate is taken out and crushed to powder after being dried. The lanthanum polystyrene sulfonate, whose weight percentage of lanthanum is 14-22%, is used as active constituents to prepare gastrointestinal tract preparations together with general amount of excipients with routine preparative method. In the invention, lanthanum polystyrene sulfonate is adopted as active constituents, mixed with excipients, and the preparation is obtained. It makes phosphate in alimentary tract become insoluble conjugates after gastrointestinal tract administration. The insoluble conjugates would be discharged. Thus, the drug can achieve the purpose of treating hyperphospheremia.