Dissolved inorganic carbon isotope(δ¹³C_DIC) is an important element to reveal the carbon cycle in lake system.Factors influencing the variation of the δ¹³C_DIC value play an important role in paleolimnological study.However, there were only few studies focusing on the spatial variation of δ¹³C_DIC from closed lakes in China.In this study, we showed the characteristics of the δ¹³C_DIC values in waters of 24 lakes on the Qiangtang Plateau(QTP) and analyzed the affected factors for their spatial variations.The δ¹³C_DIC values in the 24 lake water varied between -15.0‰ to 3.2‰, with an average value of -1.2‰.The δ¹³C_DIC values in the closed lakes show high isotopic characteristics, some even higher than the atmospheric isotopic equilibrium value.DIC concen-tration and δ¹³C_DIC value in the closed lakes were significantly higher than those in rivers, but there was no significant difference between overflowing lakes and rivers.Although lakes on QTP had high pH value and high alkalinity, the average partial pressure of dissolved CO₂ (pCO₂) in the 24 lakes was several times greater than that of the overlying atmosphere.Gas CO₂ exchange between lake water and atmosphere is an important factor influencing the δ¹³C_DIC value in closed lakes.Due to the high DIC residence time, the long time gas CO₂ exchange makes the δ¹³C_DIC value close to the atmospheric isotopic equilibrium value.For lake water with high pCO₂, degassing of dissolved CO₂ in the water makes the δ¹³C_DIC value close to or higher than the atmospheric isotopic equilibrium value.For lake water with low pCO₂, invasion of atmospheric CO₂ makes the δ¹³C_DIC value close to the atmospheric isotopic equilibrium value.