Abstract: The method based on overset unstructured grid technique is developed for the simulation of cavity flows and store separation. The numerical simulation for typical cavity flows and separation trajectory of WPFS model have achieved good agreement with experimental data and shown a promising capability for applications. The numerical simulation of door operation and store separation trajectory has been made to investigate the unsteady effects on aerodynamic characteristics of the door flap. It is found that under certain conditions, the door's movement has a strong effect on aerodynamic characteristics of the door flap, which must be seriously considered during the door flap and control system design procedure. Under current conditions, all the store separation procedure is safe. The present research provides a technical support for door flap design and store separation evaluation.