The invention discloses a method for preparing an alginic acid/attapulgite composite for sustained or controlled release tablets of a medicine. The method comprises the following steps of: dispersing acidified attapulgite into an aqueous solution to obtain a suspension at a certain concentration, slowly dripping the suspension into an aqueous solution of sodium alginate at a certain concentration, compounding at certain temperature to obtain composite slurry, acidifying, performing throwing filtration, washing, performing ethanol precipitation, performing suction filtering on the obtained composite, drying, and crushing to obtain the alginic acid/attapulgite composite. The production process is simple; a composite dehydration technology of throwing filtration first and then ethanol precipitation is adopted, so that the problem about the drying of high-water-content composites, which restricts the large-scale production is solved, and high energy consumption caused by the conventional method is reduced; and an obtained sustained or controlled release material can be directly used for tabletting to prepare matrix tablets of sustained or controlled release medicines.