The accuracy,efficiency and life of large spatial structures in orbit are affected by the plane motion,attitude and vibration. According to the structural characteristics,the sail tower space solar power station(SSPS)was simplified into a beamspringbeam model. Weak structural damping was taken into account,and dynamic equations of the model in the orbital plane were established. The coupling dynamic behaviors and damping effects of the system were analyzed by a complex structurepersevering method combining the symplectic RungeKutta method and the generalized multisymplectic method. It was found that weak damping has a slight influence on the variation of orbit radius of the spatial structure,and the ratio of the variation to the orbit radius is the order of 10-8,and the change of the attitude angle induces the deformation of nonrigid components of the system. This study extends the structurepersevering method into the dynamic analysis of complicated spatial structures,which provides theoretical references for the design and control of these systems.