Along with rapid development of railway construction in our country, it has high importance to determine the train piston wind in tunnels. From the point of functional transformation between the moving train and tunnel airflow, according to the fundamentals and basic equations of fluid mechanics and the turbulent half-experience theory, taking the train action segment as the pressure source of the piston wind, the mechanism and constitutional categories of the piston wind pressure and the influence of some conditions such as the lengths of trains and tunnels, surface rough characteristics, blockage ratio and train velocity, etc. on the piston wind are explored and the calculation method of the piston wind pressure and velocity is put forward. The calculated piston wind velocity accords with the measured result on site through making a comparison with tunnel aerodynamic test data of real vehicles. The general characteristics of the piston wind changes are derived from series combination calculations under different tunnel lengths, blockage ratios and train velocities, and from comprehensive analysis of dimensionless performance. The calculation method and performance provide important basis for full use of the piston wind.
