For the application of automatically assembling flexible space structures, this paper studies the dynamic characteristic and control design of a free-floating hub-beam system, where the rigid hub and flexible beam are the simplified models of a spacecraft and a flexible element, respectively. Based on the assumption of small deformation and low motion speed, the beam is discretized through the assumed mode method. The dynamic formulation of the system is derived by using the Lagrange equation. A PD control law with strain feedback is then designed for simultaneously tracking the desired attitude angle and suppressing the vibration of the flexible beam. Moreover, the multi?objective genetic algorithm is applied to perform the multi-objective optimization for the controller parameters. Finally, the effectiveness of the controller is verified by numerical examples.