Acid orange Ⅱ is forbidden in food industry. For food security detection of acid orange Ⅱ, the experiment based on fluorescence spectra is reported. The result shows that the emitted fluorescence range is 310～390 nm when the sample is excited by ultraviolet radiation in 230～290 nm, the peak wavelength is 350 nm, and the best excitation wavelength is 250 nm. The polarized fluorescence peak is constant, when a vertical polarizer is used. The intensity of fluorescence spectrum decreases in a linear law, with polarization angle increasing, and the polarization degree is calculated as 0.783. The orientation characteristics of molecule are considered. Moreover, analysis shows that the existence of structure of benzene and naphthalin in molecule is a reason of fluorescence, and single-line excitated state of nitrogen-bond by exciting light is another. The research can contribute to the detection of food security characteristic experssion, study of characterization of acid orange Ⅱ.