挠性空间结构周期性构型引起的低频段模态密集问题给振动控制中的控制对象建模、传感器优化配置和控制方案设计等造成困难.本文推导密频结构模态不稳定特性的产生机理,随即证明模态不稳定特性引发模型不确知性,而后基于可控性Gram矩阵的奇异值分析了密集模态的低可控度,并通过分析剩余模态的作用机理,说明模态密集将加剧溢出问题.在分析密集模态特性及影响的同时,给出控制设计中应注意的问题及可能的解决途径,对密频挠性结构在轨振动控制设计具有重要参考价值. The low-frequency mode-intensive problems caused by the periodic configuration of the flexible space structure make it difficult to model the control objects in the vibration control, the optimal configuration of the sensors and the design of the control scheme, etc. The generation mechanism of the mode-instability characteristics of the dense frequency structure , Then it is proved that the modal instability leads to the uncertainty of the model. Then, based on the singular value of the controllable Gram matrix, the low controllability of the intensive modes is analyzed. By analyzing the mechanism of the residual modes, Increase the spillover problem.While analyzing the characteristics and effects of intensive modalities, the problems that should be noticed in the control design and possible solutions are given, which is of important reference value for the in-orbit vibration control design of the dense-frequency flexible structures.