Abstract: Working out the load spectrum plays an important part in determining the fatigue life of the aircraft structure. Therefore, selection of the count method and establishment of the principle of simplification are two outstanding problems in drawing up the operational load spectrum of a fighter.To the early 1970's, the NLR method for drawing up the load spectrum of an aircraft was put forward by Dutch NLR. From the point of view of the count priciple the NLR method corresponds to the stress-strain delaying loop, so that it can give real expression to fatigue loads sustained on the aircraft, and as viewed from the principle of simplification it is a principle of invariable mean value. Based on the NLR method, we have proposed the simplification principle of variable mean value and two-wave method. Through a great deal of practical measurement and investigation in flight a typical random load history of a fighter for 50 flight hours has been given, on basis of the history the different spectra have been calculated with two count methods and four simplification principles, and the corresponding life estimation has been completed. Also the contrast tests in groups for the six different load spectra have been carried out with satisfactory results. All facts have confirmed that our theoretical analysis is useful for working out the load spectrum of the fighter with the count method and the principle of simplification.