HOBO automatic weather station，WGZ-1  photoelectric digital water table gauge and CTDP300 on-line water quality analyzer were set up to monitor rainfall, hydrochemistry and water stage at an agriculture dominated karst catchment, which  is Qingmuguan underground river systemin Chongqing China. The groundwater were sampled and analyzed monthly for hydrochemistry, Dissolved Inorganic Carbon(DIC) concentration and stable carbon isotopes (δ¹³C-DIC) in 2010. Hydrochemistry and stable carbon isotopes can verify that sulphuric acid and nitric acid take part in dissolving carbonate rocks, and the concentrations of dissolved inorganic carbon in underground river are due to the weathering of carbonate minerals by carbonic acid, sulphuric acid and nitric acid. The contribution rate that carbonic acid dissolving carbonate rocks making  DIC  largely varies from seasons, showing 62.98% in wet season and 74.86% in dry season，between 55.53% and 81.25%. In Qing Muguan catchment, the flux of DIC due to carbonic acid dissolving carbonate rocks is 14.67×10⁶ mol/a, accumulating carbon sink of 7.335×10⁶ mol/a, the flux of DIC due to carbonate rocks weathering by sulphuric acid and nitric acid is 7.48×10⁶ mol/a, amounting to a third of total DIC of ground water. Sulphuric acid and nitric acid dissolving carbonate rocks contribute to increasing DIC of 1.89×10⁶ mol/a every square kilometers of cultivated land. This result is obviously less than the values calculated by predecessors. This work shows that sulphuric acid and nitric acid derived from human activities involve in dissolving carbonate rocks and changing carbon cycling.