Abstract: The normal distribution and the Weibull distribution frequently used in reliability datum analysis and the Component Rating Factor （Rc） considering the effect of structural fatigue critical detail numbers are breifly presented in this paper.The values of statistical parameters of static strengh and fatigue life for the LY12CZ alloy ALUM are given, The computational method of the factor Rc is proven and the curve of the relation between standard deviation and specimen numbers is given by means of static and fatigue tests of over a hundred specimens.These results can be used as references in durability-damage tolerance design and reliability design of aircraft structures.