To investigate the development trends and challenges of long-endurance unmanned aerial vehicle (UAV), the research status of key technologies were analyzed and summarized. Long-endurance UAV has extensive application prospects because of its characteristics of high flight height, long operation time, and wide operation coverage. First, the representative long-endurance UAVs in the world were classified based on conventional power and new energy power, and the development history of long-endurance UAV was reviewed. Based on the demand of high lift, high lift-drag ratio, and moderate stall aerodynamic characteristics of long-endurance UAV, the large flexibility of high-aspect-ratio composite wing, and the complex mission environment of long-endurance UAV, the key technologies were analyzed, including high efficiency aerodynamic integrated design technology, aeroelastic analysis of high-aspect-ratio wing and active control technology, aeroelastic tailoring technology, flexible flight dynamics modeling and control technology, and autonomous navigation technology, etc. Finally, combined with the development situations of foreign long-endurance UAV, suggestions for the development of long-endurance UAV in China were put forward. Research shows that the conventional power long-endurance UAV has been widely used, while the new energy power long-endurance UAV is still in the prototype development stage. Technologies applied on the ultra-long-endurance UAV which has a duration of more than a week have become the focus of attention. The intelligence, collaboration, and network security of long-endurance UAV systems will be the main development directions in the future.