In order to analyze the influence of inertia effect on the dynamic characteristics of supercritical carbon dioxide dry gas seal,a mathematical model of dynamic characteristics of spiral groove dry gas seal with variable viscosity and variable density was established,and the dynamic characteristic parameters of supercritical carbon dioxide dry gas seal were solved by finite difference method and small disturbance method.The variation of dynamic characteristics of supercritical carbon dioxide dry gas seal and the influence of inertia effect on dynamic characteristics were analyzed when the operating condition is far from and close to the critical point.The results show that no matter whether the operating condition is close to the critical point or not,the dynamic characteristic coefficient increases with the increase of pressure,and the dynamic stiffness coefficient increases with the increase of rotating speed.The dynamic damping increases with the increase of rotating speed at the near critical point,but it is opposite at the far critical point.The dynamic characteristic coefficient with considering the inertia effect is lower than that without considering the inertia effect.The inertial effect can not be ignored when the operating condition is close to the critical point,and it can be ignored when the operating condition is far from the critical point.