Abstract: In order to evaluate the structural reliability under multi-level fatigue loads, an expression of residual strength is derived from the equivalent damage ratio residual strength model and the assumption that the initial strength is a random variable of any distribution. Then a stress-strength interference model under multi-fatigue loads is proposed by employing the universal generating function to calculate the probability characteristics of a function constituted by fatigue loads and residual strength. The fatigue experimental data of 45# steel is used to testify the proposed model. The results indicate that the proposed model can be used to evaluate the structural reliability under multi-level fatigue loads.