In order to study the influence of elastic characteristics of the unsprung axle bridge of the independent rotating wheelset bogie on the dynamic performance of the whole vehicle， a certain type of 100% low-floor vehicle is taken as the research object， based on the establishment of its multi-rigid body model. Considering the vibration and elastic characteristics of the axle bridge， one three-module rigid-flexible coupling dynamic model of the whole vehicle is further established. A comparative analysis of vehicle dynamic performance is carried out under random track irregularities. Compared with rigid body model， it is found from rigid-flexible coupled dynamic model that the wheel-rail lateral force and derailment coefficient is increased. the wheel-rail vertical force and wheel unloading rate is decreased. Calculation results of the axle-bridge vibration response show that the axle-bridge lateral vibration amplitude of the rigid-flexible coupling model is reduced by about 15% to the rigid body model. Results of the elastic characteristics analysis of the axle-bridge show that the vertical vibration frequency of the axle-bridge structure is 15~25 Hz. The mode shape will be excited by the wheel-rail dynamic action， which will have a great impact on the dynamic performance of the vehicle. On the basis of this research， the lightweight design of the axle bridge structure is carried out， under the premise of ensuring the constraint conditions of the dynamic performance of the vehicle and the structural strength. The geometric section is optimized and its mass is reduced by about 15%.To a certain extent， providing engineering reference for the axle bridge design of 100% low-floor vehicles.