Abstract: In order to solve the vibration suppression problem of a large flexible trussed structure, the large scale of finite element model is firstly transformed into a reduced model based on the physical reduced method of deformation modification. Then, a LQG optimal control law is designed based on the reduced model, and the closed-loop system simulation is implemented under the initial impulse force. Finally, comparing the physical reduced method with the balanced reduced method, the former one has a higher efficiency than the latter one. Furthermore, with the same active control force, the control results of the trussed structure based on the physical reduced model has obvious advantage than the control results from the balanced reduced method.