In order to evaluate operational reliability of structural components

distribution characteristic of durability load based on fixed task frequency mixing needed to be analyzed.Mathematical statistics method was used and cumulative progress of flight load was studied according to the central limiting theorem of the same distribution.Distribution function of cumulative load was deduced.It is proved that as the flight profile accumulates

distribution of durability load cumulant tends to be normal.Distribution characteristic algorithm of durability load was presented.The distribution characteristic of durability load cumulant was demonstrated by four examples of numerical simulation.Results show that relative variation coefficient decreases as the number of cumulated flight profiles increases.