The CH_4 emissions of each (domestic and industrial) wastewater treatment plants (WTP) in China in 2012 are estimated based on our field measured emission factors and detailed information of each WTP. The results show that the total emissions are 52642 tons, 39921 tons from domestic WTP and 12721 tons from industrial WTP, accounting for 75.84% and 24.16% of the total emissions respectively. Fujian, Jiangsu and Zhejiang are the top 3 emitters and Ningxia, Qinghai and Tibet are the lowest three emitters. The domestic WTP dominate the total emissions due to their high share of total COD treatment. The CH_4emissions from industrial WTP are higher than that from domestic WTP only in Jiangsu and Fujian provinces. Compared with the CH_4 emissions in 2005 reported in the Second National Communication on Climate Change of The Peoples Republic of China, the result of this paper was lower than that due to the discrepancies of activity data and emission factors. It is estimated that 99.93% and 85.94% of annual entrance COD concentration of domestic WTP and industrial WTP respectively, are lower than 1000mg/L. The low annual entrance COD concentration leads to low use of anaerobic biological treatment. The COD removed in WTP only occupies a small part of total COD removed. A large part of removed COD (64.98%) is disposed by enterprises themselves. This part is probably the predominant source of CH_4 emissions of wastewater treatment sectors in China, due to its huge volume of COD with high concentration. There is large quantity of COD released into nature, which is equivalent to one third of the COD generated in China. The emission factors research is far from sufficient in this field.