In this paper, a Schiff base L was prepared from 2,4-dihydroxyl diphenyl ketone (UV-0) and o-phenylenediamine. It was characterized by FT-IR, 1H NMR and HRMS. In the solution of V(EtOH):V(HEPES)=95:5 at pH 7.2, L displayed an “on-off” recognition ability for Fe3+ with good selectivity and without obvious disturbances by other metal ions. In the concentration range of Fe3+ from 0 to 7.0  10-5 mol/L, the intensity of this solution showed a good linear relationship with the concentration of Fe3+. According to this curve, the detection limit of L for Fe3+ was calculated to be 1.9410-7 mol/L, and the binding constant between them was 2.0104 (mol/L)-1.