Provided is a flight path calculating method for high altitude long endurance of an unmanned aerial vehicle based on regenerative fuel cells and solar cells according to an exemplary embodiment of the present invention may include a modeling step, a simulation step, and an analyzing step, and may be configured in a program form executed by an arithmetic processing means including a computer. a flight path searching method and a flight path searching apparatus for performing continuous flight path re-searching on the basis of information measured in real time during a flight of the unmanned aerial vehicle in the stratosphere to change a flight path so that the unmanned aerial vehicle may permanently perform long endurance in the stratosphere is provided.