The invention relates to the technical field of water treatment, in particular to a method for preparing carbonizing absorption grains used for purifying water. The method comprises the following steps: preparing organic materials, such as peat, sawdust, straw, bamboo dregs, and the like, and inorganic materials, such as diatomite, vermiculite, perlite, cement, and the like, according to proportion; and then mixing the organic materials and the inorganic materials with diatomite, kaolin, cement, slaked lime and the like; and adopting a high-temperature carbonizing process for forming the grains which are porous, high in absorption property, and different in sizes and shapes. The prepared grains are used for purifying polluted water.