Abstract: Based on structural strength reliability theory, a reliability analysis method of strength and stiffness of imperfect structures is proposed. The imperfect structure is defined as structure with partial element failure which does not yield a collapse mechanism and still has load bearing capability. This method considers the influence of failure elements on the reliability of imperfect structural strength or stiffness and gives equivalent safe margins. Therefore, the total failure probabilities of structural systems can be calculated at each failure state. A numerical example is studied. It is shown that such analysis is suitable for real reliability cases at each service state and the results are instructive for safety of structures in service.