Aiming to improve the accuracy of weight deduction in full-scale aircraft fatigue test, research on weight deduction technology was carried out. The weight deduction process was implemented in stages, with theoretical analysis provided for the weight deduction calculation methods involved in each stage. A weight deduction balance calculation method was proposed to further eliminate additional loads during the weight deduction process, forming a complete theoretical method for weight deduction. A series of high-precision weight deduction devices were designed, including a double-deck floor beam lever weight deduction device, a large-diameter lightweight pulley weight deduction device, and a spring system weight deduction device, all of which were verified and applied. Based on the theoretical method of weight deduction, weight deduction and weight deduction balance calculations were performed on structural parts, dummy parts, and loading equipment of a certain type of full-scale aircraft fatigue test, and verification tests were carried out in combination with high-precision weight deduction equipment. The results show that when loaded to the weight deduction load, the load error at each constraint point is less than 2 kN; in the fatigue test, the proportion of working conditions where the load error at each constraint point is less than 5 kN under air conditions is 94.9%, and the proportion of working conditions where the load error at each constraint point is less than 3% of the maximum load underground conditions is 98.9%. The theoretical method and device of this weight deduction technology improve the accuracy of weight deduction in fatigue tests, lay a foundation for the safe and stable operation of the full-aircraft fatigue test of a certain type of aircraft, and provide a theoretical reference for similar problems.