Strength Design and Research Department，AVIC Chengdu Aircraft Design and Research Institute，Chengdu 610091) Abstract：The nonlinearity of free play is common in the structure of fully moving wing, which may not only affect the validity of the ground vibration test data, but also lead to the deviation of aeroelastic stability boundary. Therefore it is necessary to carry out the aeroelastic response analysis considering the nonlinearity of free play. The free play in rotation direction of fully moving wing is taken as the research object. The fictitious mass method is used to normalize the modal shapes. Then a set of unified modal shapes that can express the whole response domain is established. The rational function is used to transform the unsteady aerodynamic force to the time domain. The limit cycle response characteristics corresponding to different parameters of free play are studied. The calculation results show that when there is free play in the fully moving wing structure system, the nonlinear oscillation phenomenon called limit cycle oscillation will occur when the velocity is lower than the linear flutter boundary. The parameters of free play will affect the amplitude and frequency of the limit cycle oscillation, as well as the entry critical velocity pressure and divergence critical velocity pressure.