<p>The piston wind induced by a high-speed train passing through tunnel accelerates the heat transfer between air inside and outside tunnel in cold regions, thereby exacerbating tunnel frost damage. It is importance for enhancing the anti-freezing capability to study the temperature distribution of a tunnel in cold regions under the influence of piston wind. However, its influence on the tunnel temperature field is always neglected in existing research. In this paper, an unsteady gas-thermal-solid coupled heat transfer model for a tunnel in cold regions considering train passing is established. The air pressure distribution and airflow characteristics in the tunnel during train passing are analyzed to reveal the mechanism and influence of piston wind on the tunnel temperature field. The results show that (1) During a train passing, air pressure field in tunnel changes significantly, inducing a high-pressure zone and a low-pressure zone at the train head and train tail, respectively. This pressure difference alters the movement and flow direction of air in tunnel. (2) Air at train head is pushed into the deeper position of the tunnel, air at the tunnel vault is squeezed and flows towards train tail, and air outside tunnel is drawn into the tunnel, leading to a significant heat exchange between air inside and outside tunnel. (3) After a train passing, air temperature at entrance section remarkably decreases, air temperature at tunnel middle drops slightly, while air temperature at exit section temporarily increases. (4) Under multiple trains passing in one day, air temperature in tunnel fluctuates considerably and rapidly, which is closely related to the convection heat transfer between tunnel lining and air during the interval of two trains passing.</p>