In order to study the dynamic detection and identification method of wheel tread flat of railway vehicle, the vehicle track coupling dynamics model and the wheel flat model were set up firstly to calculate the vehicle dynamic response. And then, the axle-box vertical vibration characteristic created by normal wheel and wheel with flat respectively was studied by improved empirical mode decomposition (EMD) and Hilbert-Huang transform (HHT), comparing the Hilbert spectrum difference between different depth and length flat wheel and the influence of running speed on Hilbert spectrum. Finally, quantitative judge the abrasion degree though wavelet package (WP) transform. The results show that the method could effectively identify wheel tread flat and without the influence of speed.