In order to investigate the effect of the transcritical state parameter changes and the real gas characteristics of supercritical carbon dioxide when flowing through dry gas seal face on the seal performance,a 3D flow model for S-CO2 at microscale spiral groove of dry gas seal was developed,and solved respectively by using Real Gas Model (RGM) and Ideal Gas Model in Fluent software.The numerical simulation results show that the choked flow is more likely to occur at the exit of the seal when considering the real gas effect of supercritical carbon dioxide.The blocking effect is increased with the increase of film gap and rotating speed,but are decreased with the increase of the medium temperature.Under the choked flow condition,the opening force and the leakage are decreased with the increase of gas temperature and rotating speed.