This paper deals with a bending and torsional vibration control method for flexible structures arranged in parallel, and a method for making a multi degree-of-freedom model by using uncontrollability and unobservability. According to these methods, it is easy to make reduced-order-models of flexible structures, and a pair of flexible structure are controlled actively by controlling each other by means of actuators placed between them. Therefore it is able to obtain enough control force under the low frequency, and control vibration of the super tall building by the strong wind. In this paper, two real structures are reduced to 4DOF models respectively including bending and torsional modes for controlling the bending and torsional vibration. These models are evaluated by means of comparing the simulated frequency response with the measured one using real structures. The effectiveness of these methods is demonstrated by the vibration control using LQ and semioptimal control theory theoretically and experimentally.