From the view of reliability, an optimal inspection model for three-dimensional structures under random loading is presented. Neuber method and finite element analysis as well as experiential stress intensity factor(SIF) were applied in the analysis of fatigue life. Based on the series system theory, the reliability function for the structural fatigue life is given. Treat the crack initiation life (CIL)as service life and the crack propagation life(CPL) as inspection period, the optimal inspection period was obtained under a given reliability. The proposed method is proved to be feasible by a numerical example, which involves a bracket under random loading.