An unstructured overset grid generation method is presented to study large amplitude movements of unconventional maneuver of an advanced fighter and a numerical method is developed based on the Navier-Stokes(N-S) equations for analyzing unsteady flow problems. Based on calculation and validation of the dynamic characteristics of a delta wing, flight attitude and velocity variation are simulated when the aircraft is under the condition of post-stall maneuvers. The numerical investigation of the unsteady vortex structure, the unsteady aerodynamics and the aerodynamic characteristics reveal the unsteady flow mechanism of the canard aircraft through Cobra maneuver.