The nonlinear flutter problem of aeroelastic system with freeplay nonlinearity has become one of the hottest and most challenging topics in the engineering field of aircraft aeroelasticity. The nonlinear aeroelastic behaviors of the control fin with freeplay nonlinearity are analyzed in the study. The reduced-order aerodynamic model in time-domain is obtained by using the minimum state approximation method, and then the nonlinear aeroelastic equations of the control fin can be obtained based on the Lagrange equation. Using the numerical method, the aeroelastic system behaviors with freeplay nonlinearity in either pitch or plunge, or both of them are studied, including limit cycle oscillations (LCOs) and nonlinear dynamic responses. The numerical results are compared with those of the equivalent linearization method. The results show that the stiffnesses of pitch and plunge springs have significant influence on the flutter boundary of the system. And when the free-plays are both in pitch and plunge, there exists complex dynamic phenomena including the multi-periodic LCOs and chaotic motions.