Abstract: In this paper it is strictly proved in theory that the standard error of the sample of, testing life which obeys logarithm-normal distribution obeys S distribution and the latter is related to the capacity of the sample. In addition,the formulas. and relevant tables are given for making the unbiased estimation of the standard error of parents population and' for calculating the safe standard error of testing life.with these formulas and tables it is able to make fatigue life and reliability analysis.This paper also deals with the concept about specification fatigue life whose standard error is the weighted average of the standard error of testing life.Using the method offered in the paper,the standard error of specification fatigue and fatigue scatter coefficient are calculated on the basis 9f testing data of the materials made in China,and the obtained standard error are in good agreement with the overage of the standard errors used in United States,Britain and Japan.