Iron is an essential trace element, which plays an important role in the life process, but excessive intake of ferric iron will reduce the oxygen carrying capacity of the body, causing unstable hemoglobin disease and methemoglobinosis. Whether from the point of view of human health or environmental protection, it is of great significance to explore a simple, rapid, sensitive and selective method for the determination of Fe(Ⅲ). Fluorescence analysis is an excellent method of molecular spectroscopy. It has the characteristics of high sensitivity, good selectivity and simple operation. It has also made good progress in the detection of heavy metal ions. At present, the determination of Fe3+ by fluorescence method has been reported, but some of them have low sensitivity, poor selectivity and toxicity of organic reagent. In this article, a simple, rapid and sensitive fluorescence method for the determination of Fe(Ⅲ) has been developed, using tetramethylbenzidine (TMB) fluorescence reagent. In pH 4.5 Tris-HCl buffer solution at 35 ℃, the reaction of H2O2-TMB was slow. When Fe (Ⅲ)was added, it catalyzed strongly H2O2 oxidization of TMB to form strong oxidized product TMBox with strong fluorescence. Using excited wavelength of 280 nm, TMBox exhibited a strong fluorescence peak at 405 nm, and the fluorescence intensity increased linearly with the increase of Fe(Ⅲ) concentration in a certain range. The fluorescence analysis conditions were optimized by univariate transformation. The pH of Tris-HCl buffer solution was 4.5, its concentration was 3.3×10-4 mol·L-1, the concentration of TMB was 3.0×10-5 mol·L-1, the concentration of H2O2 was 6.0×10-6 mol·L-1, and the reaction time was 35 min at 35 ℃. Under the selected conditions, the fluorescence signal of the system increased linearly at 405 nm with the increase of Fe3+ concentration in the range of 0.027～400 nmol·L-1. The linear equation is F405 nm=2.31c+50.0, the linear correlation coefficient R2 is 0.985, and the detection limit is 0.008 nmol·L-1. According to the procedure, the influence of coexistent substances on the determination of 200 nmol·L-1 Fe3+ was tested, with a relative error of ±10%. Results indicated that 100 times HCO-3, K+, SO2-4, NH+4, Mn2+, Na+, Cu2+, Al3+, Zn2+, F-, Mg2+, Ba2+, Ca2+, Co2+, NO3-, NO2-, 50 times CO2-3, Cr6+, 10 times Hg2+, BSA did not interfere with the determination. It showed that this Fluorescence method had good selectivity. Thus, a simple, rapid, sensitive and highly selective fluorescence method for the determination of Fe (Ⅲ) was developed. Sample solution of dairy products was prepared by the following steps: accurately absorbd 1.4 mL dairy products with 600 L acetic acid (V/V=3%), centrifugated for 3 min at 10 000 r·min-1, then took the centrifugal supernatant 1 mL with 48 L 2.5 mol·L-1 NaOH, mixed well, centrifugated for 3 min at 10 000 r·min-1, and finally piped 1 mL the supernatant, and diluted to 5 mL to get the sample solution. Then the new catalytic fluorescence method was used to determine the content of Fe(Ⅲ) in milk samples, with satisfactory results. The relative standard deviation was 0.29%～0.41%, and the recovery was 94.6%～108.0%.