Abstract: It takes a dump truck as study object. The length of the frame is very long, the elastic deformation of its frame has a significant impact on vehicle ride comfort, vehicle rigid-flexible coupling model with flexible frame are built with FEA method and virtual prototype technology. Compared with the test, the accuracy of the simulation model is verified. In order to improve vehicle ride comfort and reduce dynamic load, choosing the root-mean-square values of total acceleration of the seat, vertical acceleration of the floor and front and rear tire load as objective functions. Design parameters are analyzed by orthogonal experiment design and the second response surface model is built with secondary general rotation design. Then, An Improved Nondominate Sorting Genetic Algorithml （NSGA-II） is applied to solve the multi-objective optimization problem and the simulation verification is carried out in order to verify the rationality of optimization result. The results show that: the method better meet reduce dynamic load and improve ride comfort, which has a strong engineering practicability in the design and installation of hydro-pneumatic suspension.