The medicament for treating hyperphospheremia and preparative method thereof are provided. The medicament comprises lanthanum polystyrene sulfonate as the active ingredient and pharmaceutic adjuvant. The preparative method in the invention comprises: acidizing polystyrene sulfonate by hydrochloric acid, and soaking or eluting the obtained polystyrene sulfonic acid by water-solubility lanthanum salt solution, then washing to neutral PH by water, washing out non-exchanged redundant lanthanum ions, drying the obtained lanthanum polystyrene sulfonate and crushing to powders, the lanthanum in the lanthanum polystyrene sulfonate is 14-22 wt, and the said lanthanum polystyrene sulfonate and usual dose pharmaceutic adjuvant are prepared to the medicament suitable for gastrointestinal tract according to common preparative method. The medicament in the invention can be administered by gastrointestinal tract route, and form insolubility conjugate with phosphate in the digestive tract, then eliminate from digestive tract,, thus achieve the purpose of treating hyperphospheremia.
