The invention provides an iron, cadmium and arsenic ion adsorbent prepared after peony flower residues are modified with epoxy chloropropane components as well as a preparation method of the adsorbent and belongs to the technical field of adsorbents for metal ions in water. The preparation method comprises the steps as follows: peony flower residues are soaked in an ethanol aqueous solution, dried and crushed, and dried peony flower residue powder is obtained; the dried peony flower residue powder is placed in an acetic acid aqueous solution, bisphenol A is added, magnetic stirring is performed, and the pH of the mixed solution of the peony flower residue powder is adjusted to range from 10 to 12; epoxy chloropropane is added, constant-temperature oscillation reaction is performed at 30-50 DEG C, the product is filtered, washed to be neutral and dried, and the adsorbent for the iron, cadmium and arsenic ions is obtained. The preparation method of the adsorbent for iron, cadmium and arsenic ions is simple, the preparation cost is low, and the adsorbent is convenient to use and good in adsorption effect, does not introduce new pollutants and has bright market prospects.