An isotropic continuum damage mechanics (CDM) framework, which is developed in this paper, can provide sufficient theory of interaction mechanism of multi-damage such as brittle damage, ductile damage and creep damage. Principle of linear superposition of these different types of damage applying in engineering, which considered that these damage are independent, is not always accurate. A new creep-fatigue model which can help reliability life assessment is proposed in this paper, considering the coupling effect of fatigue damage and creep damage based on CDM.