Abstract: An online high-precision measuring device for full-size parameters of a wheel set of a rail transit vehicle, includes: a first laser sensor, a second laser sensor, a third laser sensor, and a polygon measuring module that are configured to measure multiple parts of the wheel set. The first laser sensor is arranged on an inner side of a track at a certain angle. The second laser sensor is arranged below the track at a certain angle. The third laser sensor is arranged on an outer side of the track at a certain angle. The polygon measuring module is butted with the track. The device can realize online pass-through non-stop measurement of the full-size parameters of the wheel set of the rail transit train accurately, such as tread wear, equivalent conicity and wheel polygon.