Abstract: The Sanjiang Plain is the largest marsh-wetland concentrated region in China.Located in the northeast of Heilongjiang Province,the Plain has a total marsh-wetland area of about 83.5×10⁴ hm² with rich carbon resources.Numerous rivers crisscrossing and lakes dotting this region forming vast tracts of flood plain.The study was carried out at the Ecological Experimental Station of Mire-Wetland in the Sanjiang Plain,Chinese Academy of Sciences（47°35′N,133°31′E;56 m above sea level）at the center of the Sanjiang Plain. In the region the mean annual precipitation is 550～600 mm and the annual mean temperature is 1.9 ℃.Its vegetation is mainly composed of marshes and wet meadows,and its soils are marsh soil,meadow soil and peat soil.For the study a typical type of seasonal waterlogged Deyeuxia angustifolia wet meadow was selected.The methane fluxes were measured by a closed stainless steel chamber and gas chromatography（Agilent 4890）system.The experiment lasted from June 2002 to May 2004,measuring methane fluxes twice a week,and monitoring diurnal change of the flux once a month,with three duplicates at each sample site.Meanwhile,the air temperature inside and outside the chamber, and soil temperature at the surface and 5 cm depth were also measured at the same time.The results show:there is an obviously seasonal variation and uncertain variation of the methane emission from the seasonal waterlogged Deyeuxia angustifolia wet meadow,and the methane flux was controlled by water and temperature.Two methane flux peaks appear in a year, one is in June and the other is in August or September. The methane flux from the Deyeuxia angustifolia wet meadow is averaged 0.297～18.914 mg·m^-2·h^-1 in the non-frozen season（from May to October）,and the methane emission from the Deyeuxia angustifolia wet meadow could still be detected,but much lower in flux during the frozen season（from November to April）in the Sanjiang Plain,accounting for 4.94 percent of the total of a year,which is about 0.048～2.921 mg·m^-2·h^-1.The lowest CH4 emission appear in January.