Based on the study of the developmentpattern ofhydrothermal fluids in Tengchong，Yunnan Province，we discuss characteristics ofhydrothermal activities in Tarim Basin.According to the study，theδ 13 C（PDB）vaˉlues of the CO 2 in the hot spring gases in Tengchong are between-6.4‰and-4.7‰，and the 3 He/ 4 He ratios are between1.09and3.51.The compositions of oxygen and hydrogen isotopes in hydrothermal fluids from hot spring are sim ilarwith those in meteoric water，but the oxygen isotopes show a tendency of getting heavier in theirmass.Based on the study，we believe gases from hot spring in Tengchongmainly come from deep mantle，while hydrothermal fluids originate from rainfall，which infiltrates downwards and is heated by deep heat sources and then goes upwards.According to the features of structural evolution ofTarim Basin，we believe the ShayaˉLuntai and the Yanan faulted zones in northern Tarim Basin in Late Perm ian had sim ilar geological conditions with those in Tengchong today.Under these conditions，hydrothermal fluids originating from the downward infilˉtration ofmeteoric waterwere active and strongly dissolved carbonates in the Lower Paleozoic.On the contrary，there were no sim ilar geological conditions in the Tazhong area，the Bachu area and the southern slope zone in the Tabei uplift，and thus hydrothermal dissolution was relativelyweaker.