Piston action describes the phenomenon that air at the train nose is pushed forward by the increased pressure and air at the train rear is drawn forward by the decreased pressure when a train passes through a tunnel. The variation of pressure changes the thermal environment inside the tunnel and promotes the frost damage generation in cold season. In this paper, a fluid-thermal-solid involving piston action is proposed. A high-speed railway tunnel that is located in the northeast of China is set in the background, and the influence of outside air temperature and train velocity on the thermal environment inside the tunnel are simulated and analyzed. The piston action can significantly change the temperature inside the tunnel, especially at the ends of tunnel. The temperature distribution is characterized by three zones, including disturbed zones at two sides of tunnel and undisturbed zone at tunnel middle. The freezing length is closely related to air temperature and train velocity. And also, the lengths are different at vault and rail of tunnel portal, which indicates that the anti-freezing measure should be different at these positions considering the cost. This paper can help us understand the temperature evolution process of tunnels under the action of piston wind and provide some guidelines for structural design of cold regional tunnels.