The mechanical model of the spacecraft equipped with the hoop truss deployable antenna was developed and its characteristic of dynamic responses in the stage of attitude adjustments are solved numerically. Firstly the FE model composed of the central platform, solar panels and deployable antenna was established and its natural frequencies and mode shapes in the unconstrained condition were calculated. By the union simulation of FEM and Adams the zero-order rigid-flexible coupling dynamic model of the spacecraft was set up, and then the model's translation and rotation angle as well as dynamic responses of solar panels and the deployable antenna in the process of attitude adjustments were given. Results show that the lower order mode shapes of the model are mainly from the antenna′s connecting link and solar panels′ deformation while the antenna′s shape is fixed. In the procedure of attitude adjustments, the spacecraft′s flexible attachments can deform elastically along with rigid motions and the vibration is rather serious.The antenna′s geometry central point keeps vibrating around the equilibrium position even though attitude adjustments are finished.