A method for preparing a Fenton catalyst. The method comprises the following steps: a, grinding a precursor FeCl3·6H20 into a powder; b, sealing the precursor FeCl3·6H20 powder in a crucible; c, calcinating the crucible, in which the precursor ferric chloride powder was sealed in step b, in an oven; and d, naturally cooling the crucible calcined in step c to normal temperature, and taking out a solid formed by sintering at the bottom of the crucible and grinding the same into a powder, and washing and drying the powder. The method for preparing a Fenton catalyst has a short reaction time, mild conditions, uses few raw materials, and is easily applied in large-scale industrial production. The prepared catalyst has high applicability under pH values in Fenton reactions, and still has high catalytic activity under neutral pH conditions.