Some aerodynamic characteristics of an oscillating trail-edge flap were investigated by numerical simulation, such as the unsteady effect of flow field and flow field comparison between different frequences or amplitudes. The Euler equations were solved by LU-ADI algorithm, the grid is C type grid. The numerical results showed that: (1) with the oscillation of trail-edge flap, the shock strength and its location are nonlinear to the motion of the trail-edge flap, (2) the higher the reduced frequence, the less the influence to variable pressure jump, (3) with the increase of the amplitude, the variations of shock strength and its location become more seriously.