Abstract: The composition, structure characteristics and suspension pattern of a driving-braking unit system used in high speed power bogie with double hollow axles is analyzed in this paper. During the process of motion, the relative movement between the unit and its adjacent components is analyzed and calculated in detail. It is proved that this new type of driving-braking system can satisfy the kinematical requirements of the high-speed power bogies, with the body suspension of the driving motor being achieved.