Abstract: The paper discusses the use of Weibull distribution of three-parameter to describe the fatigue life of machine element, and proposes a new method to fitting R-S-N curves under certain confidence. The parameters of three-parameter Weibull distribution are estimated by optimization, based on the samples of stress-life from tests. The fatigue life at each different reliability is then calculated under centain confidance. Thereafter the C-R-S-N curves can be fitted and the corresponding fatigue limit stress is evaluated