Toxicity and transformation process of polycyclic aromatic hydrocarbons (PAHs) is strongly depended on the interaction between PAHs and dissolved organic matters (DOM). In this study, a 125W high-pressure mercury lamp was used to simulate the sunlight experiment to explore the inhibition mechanism of four dissolved organic matters (SRFA, LHA, ESHA, UMRN) on the degradation of anthracene and pyrene in water environment. Results indicated that the photodegradation was the main degradation approach of PAHs, which accorded with the first-order reaction kinetics equation. The extent of degradation of anthracene and pyrene was 36% and 24%, respectively. DOM influence mechanism on PAHs varies depending upon its source. SRFA, LHA and ESHA inhibit the photolysis of anthracene, however, except for SRFA, the other three DOM inhibit the photolysis of pyrene. Fluorescence quenching mechanism is the main inhibiting mechanism, and the binding ability of DOM and PAHs is dominantly correlated with its inhibiting effect. FTIR spectroscopies and UV-Visible were used to analyze the main structural changes of DOM binding PAHs. Generally, the stretching vibration of N-H and C-O of polysaccharide carboxylic acid was the key to affect its binding with anthracene and C-O-C in aliphatic ring participated in the complexation of DOM and pyrene.