| Automotive body is a very important assembly of an automobile, whose mechanical characteristics are largely dependent on the structure of its body. Conducting the low-order modal analysis of the Body-in-white can not only investigate its stiffness, but also helps optimize the structure of frame body. The finite element model was build according to some car's Body-in-white. The modal analysis was performed base on the finite element model. At the same time the modal test of real car body was finished, according to the test the dynamic parameters of the Body-in-white were get. The reliability of the finite element model was validated base on the modal test. Further more, the low-order modal of the model with glass was performed. Compared with the FEA results of Body-in-white, the influence of the glass to the stiffness was the research project.To ascertain the change of the cover panel thickness of the car body to the influence of the first class frequencies, the sensitivity analysis was performed. Base on the sensitivity analysis we can get more rational design parameters in the following optimization analysis. So in the paper the concept and significance of sensitivity analysis is the main motive.In the followed optimization analysis, the parts which have more influence to the low-order modal were selected, and the thickness of these parts were set as design parameters. In the optimization design, different object functions can be designed according to different purpose. Refer to the similar researches, in this paper two object functions were designed, which were the weight of Body-in-white and the frequency values of the low-order modal.The systemic flow was established for the dynamic analysis of Body-in-white, which is "modal analysis-sensitivity analysis-optimization analysis". The flow can apply to any other similar research. The item accumulated some experience for some correlative research. The result provided a valuable consult for the further optimization of the whole body.
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