In this paper, CH(4) flux was measured from Nov. 2002 to Oct. 2005, to estimate CH(4) emissions in winter and during freeze-thaw period, and interannual variation in CH(4) emissions in freshwater marsh in northeast China. The results showed that there was an obvious CH(4) emission (0.1-2.3 mg m(-2) h(-1)) in the freshwater marsh in winter. Flux of CH(4) in winter (November to March the next year) was about 3.8%, 5.5%, and 2.2% of the whole year in 2003, 2004, and 2005, respectively. Emission of CH(4) significantly increased during the freeze-thaw period (April-June), and was about 30.8%, 20.9%, and 20.6% of the whole year in 2003, 2004, and 2005, respectively. Standing water depth greatly governed interannual variation of CH(4) emissions from marshes during the thaw-freeze period. Interannual variation of CH(4) emissions was significant during the growing season (p<0.05). Standing water depth during April to June was a primary factor, which affected the interannual variation of CH(4) flux during the growing season. Precipitation during the preceding non-growing season affected CH(4) emission indirectly via standing water depth.