The design of a robust controller for the automatic landing system is investigated for an unmanned fixed-wing aircraft based on an external navigation system. Since landing is the most difficult phase of flight, the major accidents are occurring in the phase. So, providing a high-precision automatic landing system in presence of environmental disturbances is very important for UAVs landing. The used landing navigation system is founded on a portable land-based laser-optics system which can track the UAV and calculate the altitude and direction of it toward the center of runway. However, the navigation system is external; sending them to the UAV can be done with a delay. In this regard, UAV’s control systems must be designed such that the stability of aircraft is satisfied based on information of navigation system with considering the model uncertainty, noises, disturbance and navigation delay. So in this paper, a new robust stabilizer controller is suggested for UAVs to overcome these challenges with considering some limitation in the structure of the controller. Finally, simulation results based on laboratory software in the loop been presented. The results are indicating the capability of using proposed method for automatically landing of UAVs.