Up to now,fluid inclusion is still a powerful tool to estimate the temperature and pressure of various geological processes.CO_2-bearing inclusions are commonly found in many environments.Among the CO_2-bearing inclusions,the most typical are the ternary CO_2-H_20-NaCl inclusions.These saltbearing CO_2 V-L inclusions at room temperatures are coexisting H_2O liquid +CO_2 liquid +CO_2 vapor or coexisting H_20 liquid +CO_2 liquid(or vapor).On heating they often finally homogenize to liquid phase by the bubble disappearance,and they may form CO_2 hydrate and ice during cooling.This paper reports the application of thermodynamic models,including equations of state,to ternary CO_2-H_20-NaCl fluid inclusions.Some simple equations for pressure-temperature-salinity relation on the CO_2 hydrate-liquid-vapor(liquid) surface are developed to calculate the NaCl contents(salinities) of inclusions.With these relations and the latest CO_2 solubility and PVTx models,a new iterative approach is presented to calculate the CO_2 contents of CO_2-H_20-NaCl inclusions on the assumption that the bulk molar volume of an inclusion keeps constant at the disappearances of CO_2 hydrate and vapor bubble.A prominent merit of this method is that the compositions,molar volumes and homogenization pressures of CO_2-H_20-NaCl inclusions can be simultaneously obtained without using experimental optical volume fractions of vapor bubbles at the dissociation temperatures of CO_2 hydrates.Meanwhile,the homogenization pressures and isochores of CO_2-H_2O-NaCl fluid inclusions from updated models are briefly discussed.Calculation program code for the ternary CO_2-H_2O-NaCl inclusions with microthermometric measurement and Raman analysis data as input variables can be obtained from the author. Up to now, fluid inclusion is still a powerful tool to estimate the temperature and pressure of various geological processes. CO_2-bearing inclusions are commonly found in many environments. Among the CO_2-bearing inclusions, the most typical are the ternary CO_2-H_20- NaCl inclusions. These saltbearing CO_2 VL inclusions at room temperatures are coexisting H_2O liquid + CO_2 liquid + CO_2 vapor or coexisting H_20 liquid + CO_2 liquid (or vapor) .On heating they often finally homogenize to liquid phase by the bubble disappearance, and they may form CO_2 hydrate and ice during cooling. This paper reports the application of thermodynamic models, including equations of state, to ternary CO_2-H_20-NaCl fluid inclusions. Home simple equations for pressure-temperature-salinity relation on the CO_2 hydrate-liquid-vapor (liquid) surfaces are developed to calculate the NaCl contents (salinities) of inclusions. These links and the latest CO 2 solubility and PVTx models, a new iterative approach is presente d to calculate the CO 2 contents of CO 2 -H_20-NaCl inclusions on the assumption that the bulk molar volume of an inclusion keeps constant at the disappearances of CO 2 hydrate and vapor bubble. A prominent merit of this method is that the compositions, molar volumes and homogenization pressures of CO_2-H_2O-NaCl inclusions can be taken without using experimental optical volume fractions of vapor bubbles at the dissociation temperatures of CO_2 hydrates. Meanwhile, the homogenization pressures and isochores of CO_2-H_2O-NaCl fluid inclusions from updated models are available discussed.Calculation program code for the ternary CO_2-H_2O-NaCl inclusions with microthermometric measurement and Raman analysis data as input variables can be obtained from the author.