Abstract: The activity of soil carbon metabolism enzymes has an effect on organic matter degradation and the production of humic substances, as well as an impact on soil carbon source-sink. The authors studied the relationship between four enzymes (sucrase, catalase, dehydrogenase and polyphenol oxidase) and organic carbon (TOC) and pH value, by collecting soil in Liaohe estuary coastal wetland in July, September and November of 2012. The results showed that the activity of sucrase in soil covered by Suaeda heteroptera was in the order of July＞ September＞ November, while that covered with Phragmites australis, S. heteroptera + P. australis and P. australis + Sonchus arvensis + Artemisia argyi was September＞ July＞ November. The order of catalase activity in soil covered with S. heteroptera, P. australis, S. heteroptera + P. australis and P. australis + S. arvensis + A. argyi was September＞ November＞ July. The order of dehydrogenase activity in soil covered with S. heteroptera, P. australis and S. heteroptera + P. australis was July＞ September＞ November, while, that in soil covered with P. australis + S. arvensis + A. argyi was July＞ November＞ September. The order of polyphenol oxidase activity in the soil under all the plant communities was July＞ September＞ November. The activities of sucrase, catalase, dehydrogenase and polyphenol oxidase were not significantly correlated with soil organic carbon and soil pH (P＞0.05), except that sucrase activity was significantly and positively correlated with soil organic carbon (R2=0.38, P=0.033, n=12).