The stress–strength interference model is an important method used for structural reliability design and analysis. In the stress-strength interference model based reliability analysis, the probabilistic distributions of both stress and strength must be obtained in advance. However, obtaining these two distributions, which can be representative of the real stress and strength experienced by a component, is often difficult because of the limitations in timing, budget, sample size, and testing and data acquisition capabilities. This paper is focused on the approaches of obtaining the fatigue strength distribution at a given fatigue cycle from a set of existing S-N curves, which are often obtained based on controlled load/stress. In order to achieve the goal, a fatigue S-N curve transformation technique is developed based on the fundamental statistics definition and some assumptions. The procedures of applying the technique to multiple-level, two-stress level, and one-stress level fatigue S-N curves are provided. Finally, examples of applying this technique in the stress-strength interference model based reliability analysis are also provided to demonstrate the effectiveness of the technique.