In order to predict the ride comfort and optimize the design scheme during the initial design stage，a
half car vibration model of 6 ×4 commercial vehicles is constructed by taking into account the frame flexibility，and random input running tests are simulated． Next，the influences of vehicle suspension，cab suspension，engine mount and seat suspension on the ride comfort are analyzed． Then，a frame bending model is constructed by means of the assumed mode method，and the influence of the frame flexibility on the ride comfort of a whole vehicle is revealed． Furthermore，the influence of main vehicle parameters on the ride comfort is also evaluated through sensitivity analysis． Finally，the optimal matching of primary suspension and secondary one is processed by using the particle swarm optimization (PSO) algorithm． Simulation results show that both the stiffness of the first axle suspension and the first bending vibration of frame greatly affect the ride comfort，and the cab suspension and the seat suspension contribute most to the ride comfort．