Spartina alterniflora, an invasive alien species, spreads rapidly in the coastal zones of China. It has become the most important invasive plant in coastal wetlands of China and has significant impacts on ecological structure and function of the key zone to the earth. CH_4 is an important greenhouse gas and second only to CO_2. In order to investigate effects of Spartina alterniflora invasion on CH_4 emission and reveal the potential underlying mechanisms of these effects in coastal wetlands of China, each transect was set up in the high and low marshes of wetlands in the Yangtze River estuary, respectively. A pair-wise experimental design between S. alterniflora (invasive plant) and Phragmites australis (native plant) stands in the high marsh, and S. alterniflora and Scirpus mariqueter (native plant) stands in the low marsh, was used at each site of the two transects to minimize the potential effects of background heterogeneities. Compared with native plant stands, S. alterniflora invasion significantly increased plant biomass. Invasion-increase in plant biomass was significantly higher in the high marsh than that in the low marsh, which is beneficial to carbon accumulation in the early succession of coastal ecosystem. S. alterniflora invasion also significantly increased soil moisture, soil organic carbon content, soil nitrogen content, soil microbial biomass carbon and nitrogen contents of coastal wetlands of China. CH_4 emission rates were significantly higher under S. alterniflora than P. australis stands in the high marsh, with mean values of (0.68 0.08) mg/(m~2·h) and (0.21 0.01) mg/(m~2·h), respectively. In the low marsh, mean CH_4emission rate under S. alterniflora stands was (8.31 0.50) mg/(m~2·h) during the study period, which was significantly higher than that under S. mariqueter stands ((8.31 0.50) mg/(m~2·h)). The difference in mean CH_4 emission between S. alterniflora and P. australis stands in the high marsh ((0.47 0.08) mg/(m~2·h)) was significantly lower than that between S. alterniflora and S. mariqueter stands in the low marsh ((4.37 0.48) mg/(m~2·h)). Our results indicated that the S. alterniflora invasion significantly enhanced CH_4emissions from coastal wetlands of China, probably mainly through improving the quality and quantity of substrates required for CH_4 production, increasing soil microbial biomass and moisture. The invasion-related CH_4 emissions were highly spatially variable; this variability may have been driven by the soil's anaerobic environments, induced by hydrological dynamics. These results can be applied to more reliably estimate and predict invasion-induced changes in CH_4 emissions from wetlands in the context of global climate change. These results also can provide theoretical basis and scientific support for scientific management and rational utilization of coastal zone resources as well as coping with global climate change.