Three-dimensional fluorescence excitation-emission has been widely used to characterize dissolved organic matter in municipal wastewater, lakes and rivers. However, As one of the most important pollutants in petrochemical wastewater, the fluorescence characteristics of BTEX are rarely reported. In this paper, the fluorescence spectra of 14 typical BTEX at different concentrations were studied by F-7000 fluorescence spectrometer, and the relationship between the characteristics of three dimensional fluorescence spectra and their structural characteristics was discussed. The results showed that the structure, location and number of the substituents will affect the fluorescence characteristics of BTEX. Fluorescence peaks of benzene, toluene, ethyl-benzene, n-propylbenzene, cumene, xylene and 1,2,4-trimethyl benzene located at lambda(ex)/lambda(em) =205 similar to 215/280 similar to 295 nm. A fluorescence peak of styrene located at lambda(ex)/lambda(em) = 230/345 nm. Two fluorescence peaks of phenol located at lambda(ex)/lambda(em),, = 220/300 nm, 270/295 nm. Two fluorescence peaks of aniline located at lambda(ex)/lambda(em) =235/335 nm, 280/335 nm. Chlorobenzene had a fluorescence peak locating at lambda(ex)/lambda(em) = 215/290 nm, and no obvious fluorescence peaks of nitrobenzene were found. On the conditions of 1 mg L-1 compared with benzene, the fluorescence intensity (FI) of toluene and ethylbenzene were increased by 10. 62 and 9. 45 times, with A, red shifting 5 nm, and intensity of fluorescence peaks of 1, 2,4-trimethylbenzene, three kinds of xylene enhancement ratio were 5. 49(above), 4. 87, 2. 14, 1. 33. This is mainly due to the carbon atoms of substituents which directly connected with benzene-ring expanded the rigid plane. This showed the number of carbon atoms that non coplanar and coplanar of alkyl substituents in benzene will affect the fluorescence properties of matter. When the vinyl group of styrene expanded the rigid plane, the unsaturated double bond reduced the energy required for its excitation, the fluorescence intensity of 10 mg.L-1 ethylbenzene same with the concentration of 0. 002 mg.L-1 styrene, the lambda(ex) red shifting 20 nm compared with ethylbenzene relatively. Electron donating substituents-OH and-NH2 can enhance the electron density of conjugated structure of the benzene ring. The P orbital of n electron with the benzene formation of P-pi conjugated system structure, rigid plane expansion, the intensity of fluorescence peaks increased with fluorescence spectrum redshift. On the contrary, the NO2 and Cl groups substances n-pi* transition belonged to the forbidden transition, the less number of excited state molecules, while the intersystem crossing was stronger than pi-S-1. Experimental results for weak fluorescence or no fluorescence were consistent with the theo-
