During the cyanobacteria bloom, a large amount of dissolved organic matter could be produced. The photochemical degradation is one important transformation way of algae-derived dissolved organic matter (A-DOM). In this study, the photodegradation of A-DOM, extracted from the blooming cyanobacteria in Lake Taihu, is investigated by UV-Vis spectrum and excitation emission matrix spectroscopy combined with parallel factor analysis (EEMs-PARAFAC). In addition, the effects of the light intensity, light wavelength, dissolved oxygen (DO) concentration and the initial A-DOM concentration on the photodegradation are studied. Four PARAFAC components are identified, including C1 (UVC humic-like substance), C2 (UVA humic-like substance), C3 (tryptophan-like substance) and C4 (tyrosine-like substance) with the relative abundances of 22.2%,8.6%, 68.1% and 1.1%, respectively. Under 12 h radiation by a 500 W mercury lamp, the removal percentages of a₃₅₅, C1, C2 and C3 are 70.4%, 96.1%, 85.4% and 99.2%, respectively (pH=8.0; T=28℃;[DOC]₀=10 mg/L). The photoreactivities of the three PARAFAC components follows C3 > C2 > C1. Increase in the light intensity and DO concentration is helpful for the photodegradation of A-DOM. The increase of UV light contributes most photodegradation of A-DOM. The results show that the photodegradation of A-DOM is quick and could be controlled by changing photoreaction operational parameters, which could shed light on the treatment of algae bloom and ensure the safety of drinking water.