As a result of rapid progress in the development of offensive weapons, it became necessary to build up an effective defense system against these technically advanced weapons. In this paper, it has been designed and simulates a new defense system of free-electron laser DSFEL with important advantages capable of destroying air targets (static or mobile) within a range of 70 km from the ground level. The proposed defense system consists of three main units a free electron Laser, optical lenses and control system. Numerous parameters were computed, beginning from the specification and quality of free electron Laser and atmosphere attenuation affecting on the laser beam, in addition to the quality of the target should be destroyed. The results of simulations show that the possibility of destroying any target with high precision despite the large attenuation that occurs to the laser beam such as absorption, scattering, turbulence, and reflection. It is clear through simulations that the original power of laser beam will be significantly reduced as a result of numerous and varied losses as they pass through the atmosphere. But as a final result, the laser can be used as an effective weapon to destroy long-range targets.