Abstract: Abstract：In order to reveal the variation characteristics and influencing factors of CO₂ degassing across water-air interface in karst underground river at different time scales. This study used the floating chamber- gas chromatography to monitored seasonal variation and diurnal variation of CO₂ exchange flux at the water-gas interface in Maocun, Guilin. The results were as follows: CO₂ exchange flux at the water-gas interface has obvious seasonal and diurnal variation characteristics. In addition, CO₂ is released into the atmosphere by karst underground River, which is the characteristic of atmospheric CO₂ source. On the seasonal scale, CO₂ exchange flux varies from 90.27 mg·(m²·h)^-1 to 406.32 mg·(m²·h)^-1, with an average value of 253.50 mg·(m²·h)^-1. The seasonal characteristics of CO₂ exchange flux are higher in rainy season than dry season. On the diurnal variation monitoring scale, CO₂ exchange flux varies from 46.8 mg·(m²·h)^-1 to 244.45 mg·(m²·h)^-1, with an average value of 137.81 mg·(m²·h)^-1.CO₂ exchange flux at night was significantly higher than day, the highest value appeared at 0∶00 and 1∶00 in the morning, and the lowest value appeared at 14∶00 and 15∶00 in the afternoon. The CO₂ exchange flux at the water-gas interface was affected by many factors. The correlation analysis shows that the main controlling factor of CO₂ exchange flux is the carbonate equilibrium system of Maocun underground river outlet at the seasonal scale, but the main controlling factor was the local regional environmental parameter at the diurnal scale.