A fixed-wing aircraft and flight control method and system thereof are provided. The flight control method includes steps of: setting a landing site of the fixed-wing aircraft; calculating a landing runway which starts from a runway origin and ends at the landing site and is formed by alternately connecting horizontal runways with inclined runways, wherein a horizontal distance between the runway origin and the landing site is determined according to a type of the fixed-wing aircraft, and a descent rate coefficient of the inclined runways varies with a horizontal length of the inclined runways; obtaining a current location of the fixed-wing aircraft and calculating a return route which starts from the current location of the fixed-wing aircraft and ends at the runway origin; and forming a return flight line by combining the return route with the landing runway.