An automatic landing system for fixed-wing Unmanned Aerial Vehicles (UAVs) was designed and verified by using a self-developed hardware-in-loop (HIL) simulation platform in this study. Since the landing procedure for a fixed-wing UAV is different from civil aviation, the landing data collected from real flight tests were analysed to design the automatic landing strategy. The adopted experimental platform is the Spoonbill-100 (SP-100) UAV system which was designed by the Remotely Piloted Vehicle & Micro Satellite Research Laboratory (RMRL) at National Cheng Kung University (NCKU). To boost the process of development and verification, the fuzzy logic control (FLC) was utilized to design the flight control system which includes lateral control, longitudinal control, and navigation strategy. Furthermore, an adaptive fuzzy control was applied to the altitude control for switching the membership functions of the fuzzy controller. The adaptive altitude control made the UAV have better performance during landing process. Finally, the designed automatic landing strategy and autonomous flight control was verified by using the developed HIL simulation system and a real flight test platform. The simulation and real flight test results show that the proposed automatic landing system can achieve the requirements of automatic landing procedure for SP-100 UAV.