The effects of pH values on the characteristics of photochemical degradation of dissolved organic matter (DOM) from Dianchi Lake by using UV-Visible absorption and three-dimensional excitation-emission matrix fluorescence spectroscopy (EEMs) combined with parallel factors analysis (PARAFAC) were investigated in the present study. The photochemical degradation characteristics and differences of DOM under different pH values can provide useful support for the basic data of biogeochemical cycle of DOM, and have important enlightenment for the improvement and effective control of water quality in eutrophic lakes. Three fluorescent components were identified during the process of photo-degradation of DOM (30 days), based on the split-half validation procedure. The three components identified from the fluorescence spectra were a fulvic-like fluorescence component C1 (325, 425 nm), a protein-like component (C2) (295, 390 nm) and a humic-like component (C3) (260/350, 360/450 nm)with high aromaticity. The change of pH values had important influences on the characteristics of absorption and EEM spectra of DOM in the process of photo-degradation. The results showed that the absorption coefficients of DOM increased and total fluorescence intensity decreased gradually with the increase of pH value from 4.0 to 9.0. During the 8～30 days incubation period, the intensity of fluorescent component C2 showed a trend of gradually decrease with the shift of pH value from 4.0 to 9.0, which suggested that high pH value can potentially promote photodegradation of DOM. The influences of pH values on the photo-degradation, absorption and fluorescence spectra emphasize the need for pH to be monitored and accurately controlled. It is also highly recommended that when we contrast the absorption and fluorescence data or constructing PARAFAC models among samples with different origins, the pH should be held constant to remove any potential interference of data.