As a key component of a torsion beam, the transverse beam has an important influence on the modal frequency of the torsion beam. In order to explore the mechanism of the modal frequency under large deformation of the beam structure in essence, this study provided the design reference for the torsion beam structure in the conceptual design stage and carried out the analysis on the influence of the parameters of the torsion beam cross beam on the modal frequency. The torsion beam model was abstracted as a simplified model with qualitative characteristics, and the corresponding finite element model was established by Hypermesh. The main parameters of the transverse beam such as beam horizontal position, opening direction and opening angle were selected as the research objects. The parameters of the beam structure were changed by using the Hypormorph mesh deformation and model reconstruction. The influence of the parameters on the torsion and vertical bending modal frequencies of the torsion beam was analyzed, and then the characteristic curves of the above cross beam parameters and the related modal frequencies were obtained. The analysis results indicated that the modal frequencies of the torsion beam decreased linearly with the increase of the opening angle of the beam. With the change of the opening direction of the beam, the modal frequencies of the torsion beam showed different sine. For the beam away from the Bush, the modal frequencies of torsion beams showed a downward trend. According to the analysis of the mechanism, the simplified model of the torsion beam was optimized. The modal frequency of the torsion beam can be greatly improved by optimizing the three beam structure parameters without changing the mass of the beam. The accuracy of the mechanism analysis was proved effectively.