In order to study the pollution of submerged plant litter decomposition in wetland, a 60-days litter decomposition experiment was carried out with typical submerged plants, including Ceratophyllum demersum L. (warm season plant) and Potamogeton crispus L. (cold season plant). The results showed that decomposition process of both plant litters was similar, a fast decomposition from 0 to 15 d followed by slow decomposition from 15 to 60 d. The mass loss of plant litters on 60 d reached 60.43% and 66.72%, respectively. More organic matters were obviously released from Potamogeton crispus L. than those from Ceratophyllum demersum L., while nitrogen and phosphorus release was the opposite. The nitrogen released was mainly ammonia nitrogen and organic nitrogen. Excitation emission matrix parallel factor analysis identified four kinds of fluorescence components:tryptophan-like C2, and three kinds of humus-like C1, C3, C4. The easily biodegradable tryptophan-like organic matters increased first and then decreased, while the difficult biodegradable fulvic acid-like and humic acid-like organic matters increased gradually. Three-dimensional fluorescence spectra and the maximum fluorescence intensity percentages of the four components showed that dissolved organic matter (DOM) was dominated by easily degradable organic compounds during 0-15 d and by refractory organic compounds during 15-60 d. The contents and characteristics of DOM released during the decomposition of plant litters were different, showing a low humification feature on the whole, which may be an important endogenous source of difficult biodegradable DOM in water. The decomposition of plant litters improved the microbial richness and decreased the microbial diversity in sediments. The main microorganisms included Pseudomonas (26%-35%) at 4 d, Malikia (>8%) and Bacillus (2.6%-9%) at 15 d and 30 d for decomposition, while the microorganisms that decomposed the refractory organic matter increased gradually, such as Flavobacterium. Changes in microbial community structure in sediments were influenced by changes in the availability of nutrients. The results showed that the effects of plant litter decomposition on water quality were phased. The release nitrogen and phosphorus increased during 0-15 d, which led to the deterioration of water quality temporarily; during 15-60 d, nitrogen and phosphorus release decreased, while refractory organic matter content increased gradually, which may exacerbate the humification degree of water and even sediment. Therefore, in the decay period of plant litters, it is necessary to salvage plant litters in time or manage plant harvesting rationally to avoid the deterioration of water quality caused by plant litter decay.