Many mechanical systems have the characteristics of multiple failure modes and complex failure mechanisms.On the basis of stress-strength interference (SSI) model,this paper takes the mechanical system with common cause failure (CCF) as the research object.The relationship between the stress distribution and the strength distribution is studied,and the failures of components are independent of each other under the deterministic stress.Then,the concept of conditional reliability is introduced to build the system reliability models under the action of one-stress and multi-stress for both series and parallel systems.Finally,the corresponding properties of the proposed methods are discussed to show their advantages.