In order to determine the flight boundary of unknown aircraft, a method of analyzing the aerodynamic characteristics through reverse 3d modeling and establishing a basic flight envelope is proposed, providing a technical support for the flight safety and air combat simulation of the aircraft with unknown aerodynamic parameters. Firstly, the 3d reconstruction of aircraft geometry is made by means of light and dark restoration image and engineering map reconstruction. And then the longitudinal aerodynamic characteristics are calculated and analyzed by numerical simulation. Finally, the basic flight envelope of the aircraft is calculated and verified by comparison. The results show that this complete technical approach is in support of studying the flight performance of foreign aircraft under conditions of lack of aerodynamic parameters, and the calculated flight envelope has a good reliability and can reflect the flight performance of aircraft.