Paddy fields are an important source of atmospheric methane. One of the objectives in methane researches is to estimate exactly the amount of methane emission from paddy fields. Currently there are mainly four methods: 1) extrapolation based on field measurements or specific emission coefficient and the acreage of paddy fields the value represents; reckoning by combining conversion coefficient of rice net primary production with models; conversion based on amount of organic carbon newly applied into the soil or the intrinsic soil organic carbon; and calculation by modeling. Besides, there are some other methods, like combining modeling with GIS technique or others. Spatial and temporal variation of methane emission from paddy fields are the primary factors leading to uncertainty of estimation. Statistic analysis shows that the amount methane emission emitted from the paddy fields in China is estimated at 8.4(7.2~9.5)Tg a^-1.