Abstract: The gas compositions and isotope compositions of warm springs in fault structure zones directly indicate structure activity and hydrogeochemical characteristics in the fault zones. N2 is the major gas component(90% or so) of warm springs in Tan-Lu fault belt. There is an obvious difference in δ13C CO2 for different sections of the fault zone. Theδ13C CO2 values in northern section are –4.3‰ ～7.8‰ ，and the CO2 is inorganic in origin，produced by petrochemical evolution of the rocks. Theδ13C CO2 values in central and southern sections are lower than -10‰ ，and the CO2 is organogenic. 40Ar/36Ar vary from 295 to 363，in which the lower ratios stem from atmosphere. and the higher ratios from the decay of K in the rocks of the earth crust. This paper not only studies the gas compositions of warm springs in different sections of Tan-Lu fault belt and their origin，but also is important in revealing the tectono-magmatic activity and hydrogeochemical characteristics of the fault belt.