Abstract: To explore effect of pH on rapid characterization of COD in the treatment of urban sewage using AOA-SBR technology, the three-dimensional fluorescent spectrum method was used to investigate relations between COD and fluorescence intensity of DOM, and further effect of pH on this relationship. Analyses of the three-dimensional fluorescence spectra obtained and their relationships with COD show that the DOM in the sewage under treatment contained the following three substances:tryptophan low in excitation wavelength, tryptophan high in excitation wavelength and humic acid. The two types of tryptophan and their sum in fluorescent intensity was highly and positively related to COD with R² being 0.982 3, 0.977 4 and 0.980 9, respectively, turning to be 0.871 1, 0.856 7 and 0.873 3 respectively, when pH was at 4, varying in the range of 0.926 2-0.983 4, 0.969 3-0.982 7 and 0.952 1-0.988 8 respectively, when pH varied between 6 and 8, and fluctuating in the range of 0.845 7-0.749 0, 0.900 8-0.869 9 and 0.889 5-0.837 6, respectively, along a declining trend with pH rising on above 8. Then it could be concluded that when pH was 6-8, DOM and COD concentrations are closely related in fluorescence intensity.