Abstract: This paper presents the studies on low-order time-domaindynamic modeling and active control of an offshore platform. Firstly, basedon the input-output data of the system, the method of Observer/Kalman filteridentification (OKID) is used to identify the Markov parameters of thesystem. Then a low-dimensional state-space model of the system isestablished by using the eigensystem realization algorithm (ERA). The LinearQuadratic Gaussian (LQG) controller is designed based on the low-dimensionalstate-space model. Finally, the controller designed is introduced into thefinite element model of the system to verify the effectiveness of thecontroller. Numerical results indicate the effectiveness and feasibility ofthe studies in this paper.