The study of seismic damage control was carried out for large-span space truss structures by placing viscous dampers at different locations on the roof. Time history analyses were performed with three-dimensional earthquake ground motion inputs for a gymnasium building. Taking the displacement, acceleration on the horizontal direction, member forces in the roof structure as the targets of the vibration control, the analytical results indicated that the seismic responses were effectively controlled via installing the dampers on the space truss structure. Uniformly placement of viscous dampers showed better performance when compared with that of centralized placement. The efficiency of the seismic response reduction was not linearly increasing with the damping coefficient enhancement, while there was an optimal value existing. The viscous dampers had obvious effects on vibration control of space truss structure under different earthquake intensity. The energy dissipation hysteresis curves of viscous dampers were full under different seismic waves input, and displayed the classic characteristic of velocity-dependent dampers. This study provided a valuable reference to applying the viscous dampers for seismic damage control in the long-span space structure.