In order to analyze the attitude motion of end-bodies in deployment of STS(space tether system), based on the Lagrangian equations of the second kind, the mathematical model of deployment of the system and the angular motion of end-bodies were developed, to analyze the attitude dynamics of end-bodies in deployment. Since the sizes of satellites are not negligible in actual space missions, the mother-satellite and sub-satellite connected by tether were regarded as rigid bodies with certain sizes, and the mass of the mother-satellite is much larger than the sub-satellite in modeling. Besides, the tether is regarded as a rigid rod with a certain mass. The mathematical model was used to analyze the deployment process of STS, and to analyze the main influence factors to the attitude motions of end-bodies including the initial disturbance of attitude angles, and the dynamic or static asymmetry of end-bodies. Simulation results demonstrate that either the initial disturbance or the dynamic and static asymmetry of end-bodies in deployment can cause the attitude angles instability, or even cause the tether enwinding satellites. The simulation results can provide reference for the attitude control of satellites in deployment.