Abstract: The damage of running gear caused by the wheel out of roundness of metro vehicle has attracted extensive attention. The development law of this phenomenon is studied, and the vertical vibration model of wheelset-track-floating slab is established. According to the coupled vibration model, under the action of constant braking or traction, the relationship between the circumferential radial jump and the positive pressure, creep rate of wheelset and abrasion power when there is wheel polygon out of roundness is analyzed. The influence of floating slab on wheel out of roundness is analyzed. By comparing vehicle wheel circumference in conditions with or without floating slab, it is found that floating slab can reduce the vibration of subgrade, but it has no obvious improvement for wheel out of roundness because of its large mass stiffness parameter.