Abstract: The main interest of this study is to investigate the performance of the arc-heated wind tunnel using CO2 as the test gas in order to develop heat shield materials for entering Venus and Mars atmospheres which are mainly composed of CO2 .Firstly,the mixture composition e-quilibrium of the CO2 atmospheres for a range of temperatures and pressures has been studied via the equilibrium constant method.Then,numerical simulations of the flow along the facility noz-zle have been performed using a one-dimensional isentropic method with and without freezing. The stagnation point parameters at the exit of the nozzle and theoretical performance map of the arc-heated wind tunnel with CO2 atmospheres have been calculated with one-dimensional method at the equilibrium with and without freezing,based on air envelope and neglecting the effect of arc-heater efficiency.It indicates that since the mole fraction of carbon in the arc-heated flow is as high as 30%,a large amount of carbon can be deposited onto the inside of the arc-heated wind tunnel,which can reduce the performance of insulation and heat conduction.There is a large a-mount of explosive gas CO at the exit of the nozzle no matter whether the flow is freezing or not, whose mole fraction can be as high as 50%.Therefore,it is suggested that all tests in the arc-heated wind tunnel for the simulation of CO2 atmospheres should be carried out using an addition-al inj ection gas such of N2 in the diffuser to deactivate the produced CO in order to protect the vacuum pump system and ensure the safety of people.