Abstract: Wheel flats on any tread of trains are one of the main causes that threaten safety of trains．How to measure correctly and quantitatively values of wheel flats is a key problem that must be solved in the development of high-speed and heavy load trains．Currently，there are several methods to measure wheel flats，however，almost all these methods are qualitative．Moreover，the measurement results got by these methods are greatly influenced by other factors such as the speed，the weight of the train．A totally new method to measure dynamically and quantitatively wheel flats is put forward in this paper，and both the values of wheel flats and abrasion in any tread of trains can be got when a train passes through the measuring device．The measurement system mainly consists of several sets of parallelogram mechanisms，displacement transducers and data collecting and processing system，and it was installed in the railway site．Through a lot of in-situ experiments，the accuracy of about 0.2 mm in the measurement of both wheel flat and abrasion can be obtained by the system when the moving speed of a train is less than 15 km/h．

Key words: Abrasion, Dynamic measurement Train wheels, Wheel flat