Provided is a long-endurance unmanned-aircraft oil-electric hybrid power system and control method. The long-endurance unmanned-aircraft oil-electric hybrid power system includes a sensor group, a flight control system, an energy storage lithium battery assembly, a power generation control system, a restart system, a power generation system, and a thrust propeller electromotor; the flight controlsystem controls the energy storage lithium battery assembly according to the information provided by the sensor group, the power generation control system provides electric energy for an aircraft, andthe power generation system is controlled by the power generation control system to provide electric energy for the thrust propeller electromotor and the energy storage lithium battery assembly; theflight control system also includes a takeoff subsystem, a normal flight subsystem, a charging subsystem, and a large-altitude flight subsystem; and the long-endurance cruising ability is increased through the takeoff subsystem, the normal flight subsystem, the charging subsystem, and the large-altitude flight subsystem.