Because of lightweight and super-flexible characteristics of large-scale membrane structure planar antenna， its dynamic performance parameters are complicated. In order to capture its on-orbit structure dynamic characteristics， a dynamic model of large-scale space developable membrane structure is established by the temperature-structure prestress introduction method， and the dynamic characteristics of the developable membrane structure are analyzed. Through the established dynamic model， the Eigensystem Realization Algorithm （ERA） is used to study the on-orbit identification of the modal parameters of the membrane structure planar antenna. The comparison between the identification results and simulation results shows that the ERA method can effectively identify low-order natural modes of the membrane structure plane antenna， which provides a theoretical basis for its engineering implementation.