Abstract: Based on the mechanism of delayed retardation,an analytical equation for predicting the retardation parameter has been formulated.A model for predicting tie retardation under tensile overloads and tensile-compressive overloads is put forward.We can predict the fatigue life of structures under complex spectrum loading by the present model.Numerical examples for the retardation of some specimens under different loading conditions have been carried out by the present model.The fatigue lives of the stiffened panel of a wing and the landing gear of an aircraft under spectrum loadings also have been predicted.The results quite agree with experimental data.