A tunnel-bridge-tunnel (TBT) infrastructure along the high-speed railway in China is taken as the engineering background, based on the theory of CFD and porous media, a 3D CFD numerical simulation model of train-tunnel-bridge-wind barrier-air is established. The aerodynamic load variation characteristic of the train when running on the TBT is studied. Aiming at the process of train running on the bridge-tunnel connection section (BTCS) under crosswind environment, the influence of the existence of wind barrier on the transient change effect of the aerodynamic load is further revealed from the view of the flow field. The results show that: 1) Under the condition without wind barrier, the fluctuation amplitudes of aerodynamic loads of each carriage in the process of 'from bridge to tunnel' are 1.03~1.89 times of the corresponding values in the process of 'from tunnel to bridge', and the existence of wind barrier makes the fluctuation amplitudes of aerodynamic loads in the two processes basically equal. 2) The change of train aerodynamic side force is most sensitive to the influence of the wind barrier, while the sensitivity of aerodynamic lift force and pitching moment is relatively weak.