Abstract: In this paper stastistical methods （frequency histogram, probability paper, linear regression, chi-square X2 tests） are applied to analyzing TBO of aircraft engine. The calculated results of three types of aeroengines have shown that the normal distribution is an appropriate model for TBO of aircraft engine. Therefore, along with the given value of TBO, it is reasonable to indicate the probability of the actual operating time of aircraft engines exceeding the given TBO. It is suggested to express the TBO by H（Rk%）.Thus many unnecessary overhauls can be evaded, this is of significant economical importance. The mean TBO for normal distribution H = H（50%） is recommended as the parameter of aircraft engine for overhaul. While accepting the mean TBO concept, on-condi-tion maintenance and condition monitoring technology must be adopted in engine operation in order to obtain sufficient flight safety. If the 50% actual operating time of aircraft engine is greater than the mean TBO in airline operation, the TBO can be prolonged. The method for estimating the prolonged life is also given.