Abstract: For studying the CO₂ emissions of Hongshui River Longtan Reservoir, the underway sampling was carried out to continuously survey the Longtan Reservoir of Hongshui River using a professional water sampler in July 2016. The partial pressure of CO₂(p_CO2) are calculated using the water-chemical balance and the Henry's law. The results show that the data of p_CO2 values on the surface water were divided into three intervals because the data of p_CO2 values on the surface from near the dam to the middle section ranged from 64.28 to 152.56 Pa, the transition zone of the middle section ranged from 161.57 to 257.57 Pa, as well as inflow waters ranged from 126.45 to 264.29 Pa, which was higher than that of p_CO2 before the dam. There was a significant positive correlation on surface water p_CO2 with its TDS, Cond and ORP, and a significant negative correlation on surface water p_CO2 with pH, which suggests aquatic biosynthesis-respiration, carbonate karst system are important factors affecting the change of reservoir p_CO2. Reservoir CO₂ flux had a increasing trend from the dam to the end of the tail reservoir with the mean value of the CO₂ flux being 45.96 mmol·m^-2·d^-1 and ranged from 9.06 to 78.80 mmol·m^-2·d^-1. Reservoir water showed an atmospheric CO₂ source with an obvious variation characteristics changing from weak carbon source before the dam to strong carbon source to the upstream, which implies the river type reservoir would slow down the carbon emission of river water.