Abstract: Frame systems are characterized by complexity, indeterminacy and high flexibility. In recognition of the equality between controllable Grammian matrix and observable Grammian matrix, a condensing method for active control of intelligent frame structures is proposed in this paper. An internal balancing theory is adopted to ensure controllability of system. The modes of high controllability are taken as controlling objects of a system. A discrete system model is first constructed before procurement of system control. A generalized predictive control scheme is introduced, which has better control effect on imprecise models with wnknown external forces. A numerical example is presented to show the effectiveness of the method.