In order to study the variations of dissolved carbon in Jiulongjiang River,the water samples were collected in July 2017 and January 2018,respectively,and dissolved inorganic carbon ( DIC) and dissolved organic carbon ( DOC) in rivers waters were also analyzed. The concentrations of DIC in river water are between 7.50 and 49.04 mg /L in the wet season,and the average value is 22.12 mg /L. The DIC concentrations in the dry season are between 8.84 and 84.912 mg /L and the average value is 41.17 mg /L. The DOC concentrations in the river water during the wet season are between 0.54 and 2.89mg /L,average concentration is 1.04 mg /L, dry season water DOC concentrations are and 1.34-3.56 mg /L,average concentration is 2.34 mg /L. The results show that the dissolved carbon in Jiulongjiang River has significant temporal and spatial characteristics. On the base of the discharge of Jiulongjiang River,we also calculated budget of dissolved carbon to the sea. This paper analyzes the dissolved carbon data from different tributaries in the Jiulongjiang River,combines with previous dissolved carbon data from other rivers in China,we disclose the controlling factors of dissolved carbon in river waters. And we also understand the effects of weathering of carbonate rocks, climate change, phytoplankton in rivers,and human activities on dissolved carbon concentrations in rivers.