The invention belongs to the field of preparation of functional materials, and mainly relates to a preparation method of a trivalent chromium ion adsorbent. The preparation method comprises the following steps of performing amino-functionalization on a mesoporous material by a silane coupling agent; then, enabling 2-acetylthiophene to generate Shiff base reaction with amino groups at the surface of a mesoporous material, and grafting the 2-acetylthiophene onto the mesoporous material, so as to obtain the trivalent chromium ion adsorbent with high property. The trivalent chromium ion adsorbenthas the advantages that by skillfully combining the mesoporous material and organic molecules, the adsorption ability of the mesoporous material on trivalent chromium ions can be obviously improved, and the defects of poor biocompatibility, strong toxic or side effect, difficulty in recycling and the like of the organic molecules in actual application can be overcome. The preparation method has the advantages that the preparation method is simple and flexible, the operation is easy, the practicality is high, and the application value is high.