As the large-scale spacecraft is subjected to complex loads on orbit, such as gravity gradient and thermal radiation, the thermal-dynamic coupling vibration has been induced. Therefore, the influences of gravity gradient and thermal radiation on the dynamical characteristics of the large-scale flexible beam are investigated. Firstly, based on the method of the absolute nodal coordinate and the theory of thermal-dynamic coupling, the analytical model of the lager-scale flexible beam is established; secondly, through Legendre transformation, the dual equations of this structure in Hamilton system are derived; Then through the numerical examples, it is found that the thermal flutter response may take place but its vibration amplitude is small; Furthermore, the numerical results show that the earth’s shadow has a very significant effect on the thermally induced vibration amplitude and stability of the flexible beam. Meanwhile, for a flexible beam in GEO ,it is found that the thermally induced vibration effect is greater than the gravitational gradient, and the effects of cylinder shadows and taper shadows are compared.