Abstract: Geothermal activity is an important form of earth degassing, which is frequently accompanied by a large number of greenhouse gas emissions. Taking Mapamyum of non?volcanic geothermal region in Tibet as a study case, the authors evaluated the degassing flux of geothermal soil CO2 based on the Fick's law of diffusion. The results indicate that the soil CO2 degassing flux is from 0.167 to 0.771 kg /(m2·a), while the fumarole CO2 degassing flux is from 2.054 to 7.877 kg/(m2·a) which is 18.9 times that of the soil; Compared with global volcanic soil (0.001 ~ 2.25 Mt/(km2·a), the soil CO2 degassing flux is significantly lower in value but larger than the Alpine grassland ecosystem soil CO2 emissions in the Tibetan Plateau (187.46 g(m2 a)?1)). Combined with tectonic setting, the authors evidently hold that CO2 in the geothermal system is mainly derived from magma degassing and hydrothermal fluid with walk rock alterations such as feldspathization. The low zone of soil CO2 degassing flux is constrained by the poor permeability clastic sedimentary cover.