Abstract: The conventional stress-strength interference (SSI) model is a basic model for reliability analysis of mechanical components. In this model, the component reliability is defined as the probability of the strength random variable larger than the stress random variable. But for a component under circular fatigue loads conditions, its reliability can not be calculated directly by using the SSI model. To evaluate the structural reliability under circular fatigue loads, an expression of residual strength under circular fatigue loads is derived firstly in the assumption that the initial strength is a random variable which follows any distribution. Then, a stress-strength interference model under circular fatigue loads is proposed by employing the universal generating function to calculate the probability characteristics of a function constituted by residual strength and fatigue loads. Finally, the fatigue experimental data of 45# steel is used to testify and analyze the proposed model. The results indicate that the proposed model can be used to evaluate the structural reliability under circular fatigue loads.