Disclosed is a method for preparing a granulated inorganic adsorbent for radionuclides including slurry forming, solidification, drying and hardening, granulation, and washing steps: blending a dihydrogen phosphate, a powdered inorganic adsorbent raw material and a setting time regulator in water to form a slurry; adding sintered magnesia into the slurry, and blending the mixture to form a solidified slurry; setting the solidified slurry on a disk member, and naturally drying to hardening in a specific temperature range to form a hardened solid material; smashing the hardened solid material and performing vibration sieving by using a screen to obtain a granulated inorganic adsorbent for radionuclides containing residual reagents; washing the granulated inorganic adsorbent for radionuclides containing residual reagents with water, to remove the residual reagents to complete preparation, where the adsorption capacity of the granulated inorganic adsorbent for radionuclides thus prepared is in the range of 0.7 to
