For the correlation structure existed in the multiple failure modes of component, we present a new theoretical method for reliability calculation involving failure correlation in mechanical systems. The static and dynamic calculation models based on Copulas theory were given. Since w-degree integral operation was substituted by w-degree difference operation, the calculation is simplified greatly. The reasonableness of Copulas reliability models was verified, and the problem of determining the correlation degree was solved successfully, thus the precision was ensured. In addition, the Copula theory verified the dynamic boundary continuity of reliability associated with correlation parameter, and the estimation method for the parameter of correlation degree was given. Finally, the results of a practical case study show the effectiveness and accuracy, by means of comparison with other methods.