Abstract: Dissolved organic matter (DOM)is a photochemically active material widely found in the water environments and regulates energy and material flows in ecosystems. Containing a variety of chromophores, DOM irradiated with sunlight can be photobleached and photomineralized and generate various reactive species, such as ³DOM^*, H₂O₂, ¹O₂, and HO·. These photochemical transformation processes tend to alter the microbial activity, pollutants transformation, and water quality. The source, composition, structure and properties of DOM are extremely complex, which leads to complicated photochemical behaviors and effects of DOM. To date, the relevant understanding is still lacking but constantly evolving. Here, the research advances on the photochemical behaviors of DOM and its important environmental effects were reviewed. To broaden the research object of DOM, to establish the DOM structure-photochemical reactivity relationship models, and to elucidate the influence of environmental factors on DOM photochemical effects and its mechanism were also proposed.