Peatlands are the significant source of atmospheric methane (CH4), which is produced during peat accumulation. In this study, we investigated CH4 emissions over two growing seasons from a Carex lasiocarpa-dominated peatland in the Sanjiang Plain in China using the static chamber technique. We also investigated the environmental factors controlling emissions during the two years of study, 2012 and 2013. CH4 emissions ranged from 0.07 to 56.01 mg CH4-C m(-2) h(-1) with mean values of 7.33 +/- 1.65 mg C m(-2) h(-1), showing significant temporal patterns in both years with peak values in early June and middle August respectively. Variations in water table, soil temperature at 25 cm depth and soil's water-filled pore space together explained 66.7% of the observed temporal variation of CH4 fluxes by the step-wise regression. Rapid and short-lived precipitation events might have no immediate influence on CH4 emissions, which primarily depended on the actual soil aeration and moisture conditions. A simple relationship between single parameter and CH4 fluxes would be overruled once the water table dropped below the critical threshold for CH4 release. The amount of CH4 emitted from the herbaceous peatland in the Sanjiang Plain during the growing season was about 6.93 x 10(12) mg C. Our results suggested that the herbaceous peatland in the Sanjiang Plain is an important source of atmospheric CH4.