Abstract:A modal parameter identification method and a control method of one parameter changing spacecraft caused by resulted from rotation of flexible structure are researched. Firstly, the dynamic model of spacecraft is established based on a rigid-flexible coupled spacecraft. Secondly, based on the model, a modal parameter identification method based on an improved recursive predictor-based subspace identification(RPBSID) method is used to estimate the state value. Finally, a model-free control method is used using the state value, and the effectiveness of the method is demonstrated through the simulation based on MATLAB software.