Abstract: ［Objective］ In order to ensure train operation safety and passenger comfort, it is necessary to study the changing laws of aerodynamic force and pressure inside the city railway train when passing through the variable cross-section positions in the tunnel (entering the platform, running in the tunnel, and passing through the intermediate air shaft). ［Method］ Taking the 8-carriage city railway train as an example, a numerical calculation model is established. A numerical simulation study on the aerodynamic performance at the variable tunnel cross-section is carried out, and the changes in the train body surface pressure, tunnel wall pressure, train aerodynamic force, and pressure inside the train are analyzed respectively. ［Result & Conclusion］ The changing laws of train body surface pressure and aerodynamic load are as follows: the surface pressure and lateral force with train entering the station > the surface pressure and lateral force with train passing through the intermediate air shaft > the surface pressure and lateral force when the train runs into the tunnel. The train body surface pressure amplitude is linearly related to the 1.4 ~ 2.0 power of the train running speed; the tunnel wall pressure is linearly related to the 1.79 ~ 2.10 power of the train running speed; the train body lateral force is linearly related to the 1.8 ~ 2.0 power of the train running speed, and the overturning moment is linearly related to the 1.6 ~ 2.0 power of the train running speed. The air-tightness design of the city railway train can meet the human comfort standard requirements, namely the pressure change inside the car at the variable tunnel cross-section positions shall not exceed 800 Pa per 3 seconds and 500 Pa per 1 second.