Abstract: The river carbon sink flux is important for the global carbon cycle and finding the missing carbon sink. Hydrogeological features are important parts of the karst dynamic system. In order to analyze the long-term trend and flux changes of river carbon sink, the Wuzhou section of Xijiang that was significantly affected by the wet monsoon climate was selected as the study object. In this paper, the effects of the hydrology and chemistry factors such as flow, water level, rainfall, water temperature, pH, EC, Ca²⁺, HCO^-₃ of Xijiang river basin from 2011 to 2015 on the river carbon sink flux are discussed. Results show that ① there is a good correlation of river carbon sink flux with the flow and water? level?(correlation coefficients>0.95). The carbon sink flux varies with flow and the good correlation between the carbon sink flux and water level was reflected by the effect of water level on the flow. The rainfall enters a river by different ways, which directly changes the run off in surface and further affects the river carbon sink flux.②The effect of water temperature on the river carbon sink flux was secondary and related to the climate of summer and monsoon of the Xijiang river basin during the same period. ③The pH has no obvious effect on the river carbon sink flux because the monitor point water is weakly alkaline. The EC, Ca²⁺ or HCO_3- were mainly affected by flow and have little effect on the carbon sink flux. Therefore, the flow is the most important factor for the carbon sink flux.