Abstract: Aquatic plant is an important component of lake ecosystem. With the death of aquatic plants in autumn and winter, the decomposition of their residues exerts a major effect on the cycle of biogenic elements in the lake system. Decomposition of plant residues is generally considered as a biologically driven process. However, underlying photodegradation process has been largely ignored. In this study, we investigated the removal efficiency of reed residue and the decomposition mechanism under different processes: microbial degradation, photodegradation, and the combination of bio- and photo-degradation. The result showed that, compared to single treatment of photodegradation or biodegradation, the combination of photo- and biodegradation can remove more litter mass (54.9±2.1%) and produce higher concentration of reactive oxygen species (ROS) within 110 days. In addition, we found that the removal efficiency of each litter components (cellulose, hemicellulose and lignin) exhibits positively correlation with cumulative concentration of ROS concentrations, especially the refractory component lignin. Therefore, in order to acquire more accurate prediction about the dynamics of organic carbon degradation in aquatic ecosystems，the effect of light in the decomposition process of plant residues needs to be taken into consideration. And it is necessary to obtain a deeper understanding of the decomposition mechanism of aquatic plants in shallow lakes, and this will be helpful for the scientific management and remediation of lakes.