The high CO_2 concentration in Xueyue cave,Chongqing,is rare at home and abroad.However,the circulation characteristics of carbon and its controlling factors in this cave system remain unknown.P_(CO_2-soil),P_(CO_2-cave),P_(CO_2-eq),SIc,and delta~(13) CDIC of subterranean stream were analyzed to investigate the laws of CO_2 concentration variations in Xueyu cave and its contolling factors,as well as the impact on carbon cycle in this cave by subterranean stream.It is found that soil P_(CO_2) mainly controlled by precipitation in subtropical areas was higher in rainy season than that of dry season.Cave air P_(CO_2) exhibited seasonal variations, high cave air P_(CO_2) typically occurred during warm periods,and low cave air P_(CO_2) were typical of cold periods.It was ventilation driven by the temperature difference between cave and outside air that resulted in a sharp transition of cave air P_(CO_2).Meanwhile, cave air P_(CO_2) could rise to high level in a short period of time because of CO_2 degassing from subterranean stream.Due to soil CO_2 effect,groundwater became more mineralized water with low SIc and high water P_(CO_2-eq),and dissolution in some months in rainy season.With the reduction of soil CO_2 and precipitation,groundwater had low degree of mineralization with high SIc and low water P_(CO_2-eq)in dry season.