Abstract: Based on TWINS theory，the vibration and sound radiation characteristics of the wheel/rail system of a certain urban rail transit vehicle are studied，the main factors causing the system vibration and sound radiation characteristics are analyzed. The research result shows that when the R mode is adopted as the axial mode，it will cause the wheel to vibrate substantially in the axial direction；the radiated sound power of wheel and rail will increase with the increase of speed，and the rail radiated sound power is significantly greater than wheel radiated sound power. While in tunnel state， the acoustic response is significantly greater than that in free field state，but there is little difference between the free field in the underframe area and the acoustic response.