The effects of elevated CO2 and temperature on the quantity and quality of dissolved organic carbon (DOC) of wetland sediments were investigated by measuring organic matter decomposition rates and phenolic compounds as target recalcitrant organic matter. Mean rates of anaerobic microbial metabolism were consistently higher both in vegetated sediments and in elevated CO2 and temperature, although the differences were not statistically significant (P < 0.05). Concentrations of phenolic compounds in sediments with vegetation are significantly different (P < 0.05) from those in sediments without vegetation. Regarding the biodegradability of the phenolic compounds, vegetated sediments showed higher concentrations of 2-chlorophenol and 2,4-dimethylphenol under elevated CO2 and temperature conditions, which means that more refractory material can be produced through enhanced organic matter degradation by elevated CO2 and temperature. The produced phenolic compounds can be transported to the freshwater ecosystem and influence the recalcitrance of DOC.