The invention belongs to the technical field of designs of chemical detecting methods, and particularly relates to a method for detecting flumetralin in a water body. The method comprises the following steps: firstly, preparing a standard solution; secondly, synthesizing a Fe3O4@EDTA material; thirdly, treating the flumetralin in the water body to be detected; fourthly, performing quantitative determination on the flumetralin in the water body to be detected, wherein flumetralin ions can be quantitatively detected by taking a Thermo Hypersil GOLD aQ C18 (150mm*2.1mm, 3 mu m) chromatographic column as an analytical column and taking 0.1 percent formic acid aqueous solution and methyl alcohol as a flowing phase. The method shows the advantages of MSPE; an enrichment effect is good; the detection limit of the method is reduced.