ccording to that when degradation process is linear degradation, the system is attacked by external δ shock, by considering that system failure results from external impact and natural degradation and that the natural degradation of the two is correlated, the reliability assessment of the system is proposed.The correlation is considered in two perspectives, on the one hand, the damage caused by the shock makes internal degradation increase while the magnitude of internal degradation determines the change of failure threshold value from the shock, the two affect each other.On the other hand, there is correlation between degradations.The system degradation is divided into eight parts and their incompatibility is studied, the correlation is described by Copula related theories, and the reliability function of the system is obtained.Finally, through case analysis, the validity and operability of the model are shown.