The invention provides a method for preparing a magnetic uranium adsorbent and belongs to the technical field of methods for preparing uranium adsorbing materials. The method comprises the following steps: (1) adding 0.2 g of Fe3O4 (40-80 emu/g) into ionized water and absolute ethanol, and adding ammonium hydroxide and ethyl orthosilicate under ultrasonic and agitating conditions to obtain an intermediate; (2) after adding Ca (NO3)2 and NaOH into the intermediate A under ultrasonic and agitating conditions, adding ethyl orthosilicate within 20-200 mins to obtain a magnetic adsorbent; (3) freeze-drying the magnetic adsorbent. The prepared adsorbing material is easily separated from a solution, the adsorbing performance is excellent, and the advantages of high adsorbing speed and large adsorbing capacity are represented in a wider temperature range, at different original initial concentrations and in different acid-base environments.