Abstract: The wheel diameter difference limit value is an important inspection index for metro vehicle operation and maintenance, having profound influence on vehicle operation safety and vehicle maintenance cost. The wheel diameter difference change caused by wheel wear will have large impact on vehicle traction system, braking system and dynamics performance. After analyzing the wheel diameter difference limit value of newly built metro vehicles and vehicles in operation, it is discovered that users have practically the same requirements for wheel diameter difference of newly built vehicles. The wheel diameter difference requirements under vehicle control mode and frame control mode of traction system and braking system are analyzed, and results show that under frame control mode, the larger wheel diameter difference of front and rear bogies in one vehicle has little impact on vehicle dynamics performance and basically no impact on traction system and braking system performance. It is suggested that the operation units can gradually release requirements on maximum wheel diameter difference limit value of front and rear bogies of the same vehicle under frame control mode, while monitoring and analyzing the vehicle status to finally determine the wheel diameter difference limit requirements for the front and rear bogies of the samevehicle.