The invention discloses a preparation method of an adsorbent for removing chromium ions, which comprises crushing banana stalks, adding sodium hydroxide solution to soak them, washing the banana stalk powder with water to neutrality, and adding maleic dihydrogen to the banana stalk powder cellulose. acid, add water and dry at a temperature of 80-100°C for 1-2 hours to obtain modified banana stalk powder; take water hyacinth powder and thiourea and add them to an ultrasonic stirrer, then add an appropriate amount of water for ultrasonic reaction, and place the reacted paste in Heat and dry in an oven at 60-80°C for 2-3 hours to obtain modified water hyacinth powder; add the above-mentioned modified banana stalk powder residue and modified water hyacinth powder to the mixer, add cerium ammonium nitrate and chitosan, and then add water Make it into a paste, put it into microwave heating equipment, microwave at a temperature of 120-140°C for 30-60min, cool to room temperature, and grind to obtain the chromium ion adsorbent. The adsorbent of the invention has the advantages of wide source of raw materials, low cost, large specific surface area, large adsorption capacity, high adsorption efficiency, simple preparation process, etc., and has good adsorption performance for hexavalent chromium ions.