The performance of traction control unit (TCU) directly affects the stability, dynamic response and speed range of EMUs. In order to realize the optimal design and comprehensive verification of TCU, the hardware-in-the-loop (HIL) of traction drive system was studied. The model of transformer, four quadrant convertor, traction/auxiliary inverter, asynchronous motor and vehicle dynamics were established according to mixed logical dynamic (MLD) model algorithm, reflective memory technology, main circuit topology and rational discretization method. Considering the different requirements of the simulation step, the above models were run in the central processing unit (CPU) or the field programmable gate array (FPGA) respectively. Finally, the correctness and effectiveness of the research were verified by comparison between HIL simulation results of EMUs with 4M4T and actual EMUs test results.