Abstract: Based on a real project under construction, a numerical method was carried out to analyze the influence of vehicle spaces and speed on the piston-effect in a curved tunnel. The results show that the average air speed on the cross-section in the tunnel improves significantly as the vehicle runs into and out of a tunnel. When vehicles are travelling in a tunnel, the strong backflow and a vortex can be found in the annular space between vehicles and tunnel walls, as well as the tail of vehicles. The increasing length of the vehicle space can improve the vehicle effective drag coefficient and intensify the piston effect. Under the condition of the same vehicle space, the piston wind will increase with the increase of the vehicle speed. However, the vehicle downstream will suffer seriously from the wake flow of the vehicle upstream, which will make the vehicle effective drag coefficient decline.