Abstract: In the present paper, the moment Lyapunov exponent of a binary airfoil subjected to the excitation of wide band noises is investigated. A aeroelastic model for two coupled degrees-of-freedom airfoil is established. Via the stochastic averaging method, the four-dimensional system is reduced to a two-dimensional one. Through the polar transformation, Girsanov theorem and Feynmann-Kac formula, the backword differential operator is obtained. By expanding the eigenfunctions as a Fourier cosine series, the approximate analytic expansion of the moment Lyapunov exponent is obtained. And then the Monte Carlo simulation results are given, which match the result of the approximate analytical expansion of the moment Lyapunov exponent. Finally, the influences of the system parameters, the average gas velocity and the spectral density of noises on the stochastic stability of viscoelastic plate is studied.