A numerical method is developed to simulate the unsteady flows involving moving boundaries. For this method, dynamic unstructured grid technique was used, and a MUSCL type finite volume scheme was constructed to discretize the 3D unsteady Euler equations described in ALE frame. The deformation of unstructured grid was implemented by spring analogy. The whole methodology was then applied to simulate the unsteady transonic flow of the three-dimensional rigid wing undergoing a forced sinusoidal motion in angle of attack. Computational results are in agreement with the experimental data, and the nonlinear flow characteristics caused by the fluid and structure interaction was clearly obtained. It can be concluded from the research that the whole methodology presented here is adequately accurate and reliable, and can be applied in aeroelasticity study and a series of fluid and structure interaction problems.